std vector insert begin

Insert an element at the beginning of a vector in C++

This post will discuss how to insert an element at the beginning of a vector in C++.

1. Using std::vector::insert function

The standard solution to insert an element to a vector is with the std::vector::insert function. It takes an iterator to the position where the element needs to be inserted. To insert an element at the beginning of a vector, pass an iterator pointing to the first element in the vector. For example,

main() std::vector<int> v = {2, 3, 4, 5}; int target = 1; // add target at beginning v.insert(v.begin(), target); // print vector std::copy(v.begin(), v.end(), std::ostream_iterator<int>(std::cout, " ")); return 0;

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Output: 1 2 3 4 5

2. Using std::rotate function

Alternatively, we can append the element at the vector’s end and then rotate the vector to the right by 1 position. A typical implementation of this approach would look like this:

main() std::vector<int> v = {2, 3, 4, 5}; int target = 1; // add target at beginning v.push_back(target); std::rotate(v.rbegin(), v.rbegin() + 1, v.rend()); // print vector std::copy(v.begin(), v.end(), std::ostream_iterator<int>(std::cout, " ")); return 0;

3. Using std::deque

To add and remove elements from both the front and the end of a container, consider using a std::deque . It implements a Double-ended queue that can expand or shrink on both ends. To insert an element at the beginning, use the push_front member function of std::deque , as shown below:

main() std::deque<int> d = {2, 3, 4, 5}; int target = 1; // add target at beginning d.push_front(target); // print vector std::copy(d.begin(), d.end(), std::ostream_iterator<int>(std::cout, " ")); return 0;

That’s all about inserting an element at the beginning of a vector in C++.

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C++ Tutorial: A Beginner’s Guide to std::vector, Part 1

This C++ tutorial is meant to help beginning and intermediate C++ programmers better understand the standard template class in the C++ programming language. Interested in learning more about C? Visit the TechRepublic Academy.

Using C++ Vectors

The final technical vote of the C++ Standard took place on November 14th, 1997; that was quite a while ago. However, significant parts of the Standard, especially the Standard Library, are still not very popular among many C++ users. A constant reader of CodeGuru’s C++ forums may notice that many questions and answers still imply hand-crafted solutions that could be very elegantly solved by using the Standard Library.

One issue that comes up very often is the use of C-style arrays, with all their problems and drawbacks. People seem to be scared of the standard vector and its brother deque . One reason might be that the Standard Library documentation is mostly pretty elliptic and esoteric.

In this article, I will discuss C++ vectors and try to explain them in a way that is more accessible and understandable. I do not claim that this article is by any means complete; it is meant to give you a start in using vectors in C++ and to help you avoid the most common pitfalls. We will start small and will not try to handle the topic very academically.

Introduction to vector in C++

Vector is a template class that is a perfect replacement for the good old C-style arrays. It allows the same natural syntax that is used with plain arrays but offers a series of services that free the C++ programmer from taking care of the allocated memory and help to operate consistently on the contained objects.

The first step using vector is to include the appropriate header:

Note that the header file name does not have any extension; this is true for all of the Standard Library header files. The second thing to know is that all of the Standard Library lives in the namespace std . This means that you have to resolve the names by prepending std:: to them:

For small projects, you can bring the entire namespace std into scope by inserting a using directive on top of your . cpp file:

This is okay for small projects, as long as you write the using directive in your .cpp file. Never write a using directive into a header file! This would bloat the entire namespace std into each and every .cpp file that includes that header. For larger projects, it is better to explicitly qualify every name accordingly. I am not a fan of such shortcuts. In this article, I will qualify each name accordingly. I will introduce some typedef s in the examples where appropriate—for better readability.

What is std::vector in C++

What is std::vector<T> v; ? It is a template class that will wrap an array of Ts. In this widely used notation, ‘T’ stands for any data type, built-in, or user-defined class. The vector will store the Ts in a contiguous memory area that it will handle for you, and let you access the individual Ts simply by writing v[0] , v[1] , and so on, exactly like you would do for a C-style array.

Note that for bigger projects it can be tedious to repeatedly write out the explicit type of the vectors. You may use a typedef if you want:

Do not use a macro!

For the beginning, let’s see what a vector can do for us. Let’s start small and take the example of an array of integers. If you used plain arrays, you had either a static or a dynamic array:

Let’s do the same thing using a vector :

As you see, vector combines the advantages of both the static and the dynamic array because it takes a non-const size parameter such as the dynamic one and automatically deletes the used memory like the static one.

The standard vector defines the operator [] , to allow a “natural” syntax. For the sake of performance, the operator [] does not check whether the index is a valid one. Similar to a C-style array, using an invalid index will mostly buy you an access violation.

In addition to operator [] , vector defines the member function at() . This function does the same thing as the operator [] , but checks the index. If the index is invalid, it will throw an object of class std::out_of_range .

Depending on the implementation of the C++ Standard Library you use, the above snippet will print a more or less explicit error message. STLPort prints the word “vector”, the Dinkumware implementation that comes with Visual C++ prints “invalid vector<T> subscript”. Other implementations may print something else.

Note that vector is a standard container. The controlled sequence also can be accessed using iterators. More on iterators later in this article. For now, let’s keep it simple.

Now, what if you don’t know how many elements you will have? If you were using a C-style array to store the elements, you’d either need to implement a logic that allows a developer to grow your array from time to time, or you would allocate an array that is “big enough.” The latter is a poor man’s approach and the former will give you a headache. Not so vector :

In the previous example, push_back() appends one element at a time to the array. This is what we want, but it has a small pitfall. To understand what that is, you have to know that a vector has a so-called ‘controlled sequence’ and a certain amount of allocated storage for that sequence. The controlled sequence is just another name for the array in the guts of the vector . To hold this array, vector will allocate some memory, mostly more than it needs. You can push_back() elements until the allocated memory is exhausted. Then, vector will trigger a reallocation and will grow the allocated memory block. This can mean that it will have to move (that means: copy) the controlled sequence into a larger block. And copying around a large number of elements can slow down your application dramatically. Note that the reallocation is absolutely transparent for you (barring catastrophic failure—out of memory). You need to do nothing; vector will do all what that takes under the hood. Of course, there is something you can do to avoid having vector reallocate the storage too often. Just read on.

In the previous example, we declared the vector using its default constructor. This creates an empty vector . Depending on the implementation of the Standard Library being used, the empty vector might or might not allocate some memory “just in case.” If we want to avoid a too-often reallocation of the vector ‘s storage, we can use its reserve() member function:

The parameter we pass to reserve() depends on the context, of course. The function reserve() will ensure that we have room for at least 10 elements in this case. If the vector already has room for the required number of elements, reserve() does nothing. In other words, reserve() will grow the allocated storage of the vector , if necessary, but will never shrink it.

As a side note, the following two code snippets are not the same thing:

The first snippet defines a vector containing 10 integers, and initializes them with their default value (0). If we hadn’t integers but some user-defined class, vector would call the default ctor 10 times and contain 10 readily constructed objects. The second snippet defines an empty vector , and then tells it to make room for 10 integers. The vector will allocate enough memory to hold at least 10 integers, but will not initialize this memory. If we had no integers, but some user-defined class, the second snippet wouldn’t construct any instance of that class.

To find out how many elements would fit in the currently allocated storage of a vector , use the capacity() member function. To find out how many elements are currently contained by the vector , use the size() member function:

This will print

That means that the number of elements that can be added to a vector without triggering a reallocation always is capacity() – size() .

Note that, for the previous example, only 0 is a valid index for array . Yes, we have made room for at least 10 elements with reserve() , but the memory is not initialized. Because int is a built-in type, writing all 10 elements with operator [] would actually work, but we would have a vector that is in an inconsistent state, because size() would still return 1. Moreover, if we tried to access the other elements than the first using array.at() , a

std::out_of_range would be thrown. At a first sight, this may seem inconvenient, but a closer look reveals why this is so: If the vector contained objects of a user-defined class, reserve() wouldn’t call any ctor. Accessing a not-yet-constructed object has undefined results and is a no-no in any case. The important thing to remember is that the role of reserve() is to minimize the number of potential reallocations and that it will not influence the number of elements in the controled sequence. A call to reserve() with a parameter smaller than the current capacity() is benign—it simply does nothing.

The correct way of enlarging the number of contained elements is to call vector ‘s member function resize() . The member function resize() has following properties:

Another way to enlarge the number of controlled elements is to use push_back() . In certain cases, this might be more efficient than calling resize() and then writing the elements. Let’s have a closer look under the hood of vector , by looking at the following example:

The two versions are equivalent, meaning that they will produce the same result. In both cases, we start with an empty vector . In the first version, we use resize() to grow the size of the controlled sequence to 10 elements. This will not only reallocate the vector s storage, but will also construct a sequence of 10 elements, using the default ctor of X. When resize() is finished, we will have 10 valid objects of type X in our vector , all of them having val_ == 0 , because that’s what the default ctor of X does. In a second step, we pick every X in the sequence and use X::set() to change its val_ .

In the second version, we call reserve() to make room for 10 elements. The vector will reallocate its storage and do nothing more than that. No element is constructed yet. In a second step, we create 10 objects of type X using the second ctor, thus giving them directly the correct value, and push_back() them into the vector.

Which method is more efficient? That probably also depends on the implementation of the Standard Library, but the second version is likely to be slightly more efficient because it doesn’t call X::set() for each element.

Now that we have seen how to declare a vector and how to fill it up, let’s see how we can operate on it. We will start with an analogy to C-style arrays and will progressively discover other possibilities, that are better or safer.

There are two ways of accessing a C-style array: either by using the subscript operator, or by using pointers. Also, passing a C-style array to a function means passing a pointer to the first element. Can we do the same thing with a vector ? The answer is yes. Let’s take a small example:

When we say mean(a, 5) , the first parameter actually is the address of the first element in the array &a[0] . We know that a vector is required to keep its elements in a contiguous block of memory, in order. That means that we can pass the address of the first element of a vector to the function mean() and it will work:

That’s nice, but it’s still not quite the same. We were able to directly initialize the C-style array, but we had to push_back() the elements into the vector. Can we do better? Well, yes. We cannot directly use an initializer list for the vector , but we can use an intermediary array:

Here we use another constructor provided by vector . It takes two parameters: a pointer to the first element of a C-style array and a pointer to one past the last element of that array. It will initialize the vector with a copy of each element in the array. Two things are important to note: The array is copied and it does not somehow go into the possession of the newly created vector , and the range we supply is from the first element to one past the last element in the array.

Understanding the second point is crucial when working with vector s or any other standard containers. The controlled sequence is always expressed in terms of [first, one-past-last) —not only for ctors, but also for every function that operates on a range of elements.

When taking the address of elements contained in a vector , there is something you have to watch out for: an internal reallocation of the vector will invalidate the pointers you hold to its elements.

In the previous example, we take the address of the fourth element of the vector and store it in pi . Then we push_back() another element to the end of the vector . Then we try to use pi . Boom! The reason is that push_back() may trigger a reallocation of v ‘s internal storage if this is not large enough to hold the additional element, too. pi will then point to a memory address that has just been deleted, and using it has undefined results. The bad news is that the vector might or might not reallocate the internal storage—you can’t tell on the general case. The solution is either not to use pointers that might have been invalidated, or to make sure that the vector won’t reallocate. The latter means to use reserve() wisely in order to have the vector handle memory (re)allocation at defined times.

From the member functions we have seen so far, only push_back() and resize() can invalidate pointers into the vector . There are other member functions that invalidate pointers; we will discuss them later in this tutorial.

Note that both the subscript operator and the member function at() never invalidate pointers into the vector .

Speaking of pointers into the vector , we can introduce a standard concept at this point: iterators . Iterators are the way the Standard Library models a common interface for all containers— vector, list, set, deque , and so on. The reason is that operations that are “natural” for one container (like subscripting for vector ) do not make sense for other containers. The Standard Library needs a common way of applying algorithms like iterating, finding, sorting to all containers—thus the concept of iterators.

An iterator is a handle to a contained element. You can find an exact definition in your favorite textbook, if you want. The internal representation of an iterator is irrelevant at this point. Important is that if you have an iterator, you can dereference it to obtain the element it “points” to (for vector the most natural implementation of an iterator is indeed a plain vanilla pointer—but don’t count on this). Let’s get a grip on iterators with a small example:

Let’s take this small program step by step:

This declares a const iterator i for a vector<double> . We are using a const iterator because we do not intend to modify the contents of the vector .

The member function begin() returns an iterator that “points” to the first element in the sequence.

The member function end() returns an iterator that “points” to one-past-the-last-element in the sequence. Note that dereferencing the iterator returned by end() is illegal and has undefined results.

You can advance from one element to the next by incrementing the iterator.

Note that the same program, but using pointers instead of iterators, leads to a very similar construct:

So, if we can use pointers to basically achieve the same thing in the same way, why bother with iterators at all? The answer is that we have to use iterators if we want to apply some standard algorithm, like sorting, to the vector . The Standard Library does not implement the algorithms as member functions of the various containers, but as free template functions that can operate on many containers.

The combination of standard containers in general (and vector in particular) and standard algorithms, is a very powerful tool; unfortunately, much too often neglected by programmers. By using it you can avoid large portions of hand crafted, error-prone code, and it enables you to write compact, portable, and maintainable programs.

Let’s have a look at the member functions vector provides:

C++ Vector Functions: Constructors

A complete set of C++ constructors , C++ destructor , and copy operator is provided. Let’s have a look at them on the example of a vector of standard strings:

The assign() function in C++

The assign() function will reinitialize the vector. We can pass either a valid element range using the [first, last) iterators or we can specify the number of elements to be created and the element value.

The assignment completely changes the elements of the vector . The old elements (if any) are discarded and the size of the vector is set to the number of elements assigned. Of course, assign() may trigger an internal reallocation.

Stack operations in C++

We have seen the function push_back() . It appends an element to the end of the controlled sequence. There is a counterpart function, pop_back() , that removes the last element in the controlled sequence. The removed element becomes invalid, and size() is decremented. Note that pop_back() does not return the value of the popped element. You have to peek it before you pop it. The reason why this is so is exception-safe. Popping on an empty vector is an error and has undefined results.

Note that pop_back() does not shrink the capacity() .

Predefined iterators in C++

We have seen the iterators begin() and end() . They point to the first, respectively, to one-past-the-last element in the controlled sequence. There also are rbegin() and rend() which point to the first, respectively, to the one-past-the-last element of the reverse sequence. Note that both rbegin() and rend() return the type reverse_iterator (or const_reverse_iterator for their const versions)—which is not the same as iterator , (respectively const_iterator ). To obtain a “normal” iterator from a reverse iterator, use reverse_iterator ‘s base() member function:

Element Access in C++

We have seen the subscript operator [] that provides unchecked access and the member function at() , which will throw an object of type std::out_of_range if the index passed is invalid. Two other member functions exist, front() and back() , which return a reference to the first, respectively the last element in the controlled sequence. Note that they do not return iterators!

Note that we cannot write *(–v.end()) because v.end() is not a l-value.

List Operations in C++

A few operations provided by vector are actually native for list . They are provided by the most containers and deal with inserting and erasing elements in the middle of the controlled sequence. Let’s demonstrate them by some examples:

Note that both insert() and erase() may invalidate any iterators you might hold. The first version of insert() returns an iterator that points to the inserted element. The other two versions return void . Inserting elements may trigger a reallocation. In this case, all iterators in the container become invalid. If no reallocation occurs (for example, by a call to reserve() prior to inserting), only iterators printing between the insertion point and the end of the sequence become invalid.

Erasing elements never triggers a reallocation, nor does it influence the capacity() . However, all iterators that point between the first element erased and the end of the sequence become invalid.

Calling clear() removes all elements from the controlled sequence. The memory allocated is not freed, however. All iterators become invalid, of course.

Note that both insert() and erase() are not very efficient for vector s. They are expected to perform in amortized linear time, O(n)+. If your application often uses insertion and erasure, vector probably isn’t the best choice of a container for you.

Comparison Operations in C++

You can compare the contents of two vectors on an element-by-element basis using the operators ==, != and < . Two vector s are equal if both have the same size() and the elements are correspondingly equal. Note that the capacity() of two equal vector s need not to be the same. The operator < orders the vector ‘s lexicographically.

Swapping Contents in Vectors Using C++

Sometimes, it is practical to be able to swap() the contents of two vectors. A common application is forcing a vector to release the memory it holds. We have seen that erasing the elements or clearing the vector doesn’t influence its capacity() (in other words, the memory allocated). We need to do a small trick:

Normally (see below), vector s simply swap their guts. In the previous example, we create a temporary vector by using the copy ctor and swap() its contents with v . The temporary object will receive the entire memory held by v and v will receive the memory held by the temporary object—which is likely to allocate nothing on creation. The temporarily created vector is destroyed at the end of the above statement, and all the memory formally held by v is freed.

The vector class template has a second, default template parameter:

The allocator is a class that supplies the functions used by the container to allocate and deallocate memory for its elements. In this tutorial, we assumed that we have a default allocator and we will continue to assume this. For the sake of completeness, note that swap() will perform in constant time (simply swap the guts of the two vector s) if both allocator s are the same. This is in most cases so.

In this first tutorial, we have scratched the surface of the Standard Library and met std::vector . In the next tutorial, we will have a look at more advanced topics related to vector , respectively applying standard algorithms to it, and will discuss design decisions, such as the question of when to store objects and when to store pointers to objects in the vector . We also will introduce a close relative of the vector , that is, std::deque .

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vector insert() Function in C++ STL

std::vector::insert() is a built-in function in C++ STL that inserts new elements before the element at the specified position, effectively increasing the container size by the number of elements inserted.

Time Complexity – Linear, O(N)

The insert function is overloaded to work on multiple cases which are as follows:

1. Insert an Element at the Given Index

Syntax of insert() in vector.

The function accepts two parameters specified below:

Example of insert() in vector

2. Insert Multiple Elements at Given Index

The function accepts three parameters specified as below:

size – It specifies the number of times a val is to be inserted at the specified position.

Example of insert() in Vector

3. Insert the Range of Elements at Given Index

Syntax of vector insert().

The function accepts three parameters specified below:

Example of Vector insert()

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How to insert an element of vector2 and int to a hash table?

I am trying to make a hash table that takes on a Vector2 as its key and an int as its value, but when I try to insert a key and value pair in its insert function I get an error:

If anyone knows why this is happening and how to fix it, please help.

I tried to use a different way to insert that is:

but it only gives me another error:

Vector2 is a vector class that takes to integers x and y.

data-structures

It seems that your Vector2 class does not provide a copy constructor. Without it, I got the very same error message.

Live demo: https://godbolt.org/z/ca7r96roe

As for the second problem, you are trying to push_back into a vector element, which type is std::pair . std::pair does not have a push_back member function. Maybe, you wanted something as:

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Programming Tutorials

Inserting a single element at specific position in vector

We are going to use first overloaded version of Vector’s insert() function i.e.

It Inserts a copy of give element “val” , before the iterator position “ pos ” and also returns the iterator pointing to new inserted element.

Frequently Asked:

Let’s understand by example,

Suppose we have a vector of int i.e.

Now we want to insert an element at index position 4th (In vector position index start from 0),

Vector’s contents will be now,

Best Resources to Learn C++:

Inserting an element in vector will increase the vector size by 1. As in vector all elements are stored at continuous memory locations, so inserting an element in between will cause all the elements in right to shift or complete reallocation of all elements.

Inserting multiple elements or a range at specific position in vector

Some times we encounter a situation where we want to insert multiple elements in vector at specific position. These multiple elements can from another vector , array or any other container.

For this, vector provides an overloaded version of insert() function to insert multiple elements i.e.

It inserts the elements in range from [first, end) before iterator position pos and returns the iterator pointing to position first newly added element.

Let’s understand by an example,

Suppose we have 2 vectors of strings i.e.

Now insert all the elements in vec2 at position 3 in vec1 i.e.

Contents of vec1 will be now,

Inserting multiple elements using Initializer list

Another overloaded version of vector’s insert() function is as follows,

It copies all the elements in given initializer list before given iterator position pos and also returns the iterator of first of the newly added elements.

Suppose we have vector of int i.e.

Let’s add all elements in initialisation list to the existing vector i.e.

Contents of vecOfInts will be now,

vector.insert() and Iterator invalidation

Inserting elements in vector will cause existing elements to shift places or sometimes complete reallocation, which will invalidates all the existing iterators.

Complete example is as follows,

To Compile the above example in linux use following command,

g++ –std=c++11 example.cpp

About Jonathan Boccara

Hello, my name is Jonathan Boccara, I'm your host on Fluent C++. I have been a developer for 10 years. My focus is on how to write expressive code . I wrote the book The Legacy Code Programmer's Toolbox . I'm happy to take your feedback, don't hesitate to drop a comment on a post, follow me or get in touch directly !

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How to Insert Several Elements in a Vector (With No Memory Errors)

Inserting elements in a vector sounds like the most basic use case we can think of when it comes to using collections in C++.

Nevertheless, this is a complex topic in itself, because std::vector offers various ways to insert several elements. Choosing the most appropriate depending on your exact use case allows to write more expressive code. And misusing the interface of std::vector can lead to memory errors.

Let’s navigate the various ways to insert several elements in a vector in a safe way, so that you can choose the one that fits best for your code.

Inserting several values from a range

The simplest case is when the elements you want to insert in a vector are themselves part of a range, that is to say that they’re between two iterators.

In this case we can use the range insert in the destination vector:

If we print the contents of destination we get:

Inserting in reverse order

If ever you’d like to insert the elements of the source in reverse order, the range insert function of vector is of no use here. We’ll see later that this is not the case for other use cases.

To insert in reverse order, we need to operate a reverse operation on the source, for example by using reverse iterators:

As a result destination contains the following values:

Inserting several values one by one

Let’s now examine the use case of inserting several values but that don’t come from a range. That is to say, we’d like to insert them one by one.

In this case we need to be careful in order to insert them in the order we want (in order or in reverse order). Paradoxically, the code is slightly simpler to insert in reverse order, so let’s start with this case.

Here is the most simple code (I can think of) to insert several values in reverse order with standard C++:

It is interesting to note that, when glancing at it, this code may not look like it’s inserting in reverse order. Indeed, it seems to use the same code to insert 1, then 2, etc.

Of course when you run the code in you head you find that it inserts each new value at the same position as the previous one, which shifts forward the previously inserted values. But code that needs to be run in our head to be understood is not the most expressive code.

Another interesting point to note is that there is a repetition of the expression begin(v) + 1 . And in general, we want to avoid duplicated logic in code.

So it may be tempting to replace this expression with an intermediary value:

But this code has a bug. Can you see it?

(leaving you a bit of time to find the bug for yourself)

When we run this code , we get the following output:

This is a memory error.

The problem is that after adding some values to the vector, the vector needs to reallocate its elements to a location in memory where there is more space in order to store all the values. This implies that the position iterator, pointing into the original location of the vector, becomes invalid. Using it results in undefined behaviour, leading to the memory error we see here.

Now would this error happen in real life? It certainly happened to me, when designing the insert pipe in the pipes library ! This is what motivated me in the first place to analyse the various use cases of insertion in a vector and write this article.

So do we have the repeat the begin(v) + 1 expression?

Another way is to take advantage of the returned value of the insert member function of std::vector . insert returns the position of the inserted element. And this is a valid iterator, even if the vector reallocated its storage:

Is this better than begin(v) + 1 ? It reduced code duplication, but it increased code in total. I’m not sure which one is the best alternative here. It’s not that important anyway, the most important point here is to avoid the above memory error.

Inserting in order

To insert several individual values in order in a vector, we can use the insert interface this way:

If we print the collection we get this:

This code is less robust than its counterpart to insert in reverse order that repeated begin(v) + 1 . Indeed, if we need to change the code and add a new value between the existing ones, we have to remember to update the positions of all the other insertions down the line:

There is coupling between the lines of code, and coupling leads to all sorts of problems .

How can we rewrite this code to make the addition of an intermediary line more straightforward?

Unfortunately I don’t know an elegant way here. The only solution I can see is to adapt the code that used the return value of insert . The adaptation consists in inserting the new value after the position returned by the previous insertion:

Then to add a new value we can just add a new line:

But, this doesn’t look like welcoming code! If you can see a better solution, I’d be happy if you let me know in the comments section.

In any case, what is certain is that it is beneficial to know well the interface of std::vector , especially since this is the most commonly used container in C++. The better you know it, the easier you can write expressive and correct code for each of the use cases you encounter.

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Std:: insert_iterator.







(C++20)

(C++20)
(C++11)





(C++20)




(C++17)
(C++11)
(C++11)

Iterator concepts


output_iterator_tagforward_iterator_tagbidirectional_iterator_tagrandom_access_iterator_tagcontiguous_iterator_tag (C++20)



iter_difference_titer_reference_titer_const_reference_titer_rvalue_reference_titer_common_reference_t (C++20)(C++20)(C++23)(C++20)(C++20)

indirectly_regular_unary_invocable (C++20)



default_sentinel (C++20)
unreachable_sentinel (C++20)

cbegin (C++14)
cend (C++14)
ssize (C++20)

crbegin (C++14)
crend (C++14)

Member functions



insert_iterator::operator++(int)


< class Container > class insert_iterator : public < , void,void,void,void >		(until C++17)
< class Container > class insert_iterator;		(since C++17)

std::insert_iterator is a LegacyOutputIterator that inserts elements into a container for which it was constructed, at the position pointed to by the supplied iterator. The container's insert() member function is called whenever the iterator (whether dereferenced or not) is assigned to. Incrementing the std::insert_iterator is a no-op.

Member types Member functions Member objects Example See also

[ edit ] Member types

Member type

Definition

void

void	(until C++20)
	(since C++20)

Member types , , , and are required to be obtained by inheriting from < , void, void, void, void>.

(until C++17)

[ edit ] Member functions

	constructs a new (public member function)
	inserts an object into the associated container (public member function)
	no-op (public member function)
operator++(int)	no-op (public member function)

[ edit ] Member objects

Member name	Definition
(protected member object)	a pointer of type
(protected member object)	an iterator of type (until C++20) (since C++20)

[ edit ] Example

[ edit ] see also.

	creates a of type inferred from the argument (function template)
	iterator adaptor for insertion at the end of a container (class template)
	iterator adaptor for insertion at the front of a container (class template)

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<climits> (limits.h)
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<csetjmp> (setjmp.h)
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<cstdlib> (stdlib.h)
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<ctime> (time.h)
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<cwchar> (wchar.h)
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Containers:

C++11 <array>
<deque>
C++11 <forward_list>
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<map>
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C++11 <unordered_map>
C++11 <unordered_set>
<vector>

Input/Output:

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<ios>
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<iostream>
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Multi-threading:

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C++11 <condition_variable>
C++11 <future>
C++11 <mutex>
C++11 <thread>
<algorithm>
<bitset>
C++11 <chrono>
C++11 <codecvt>
<complex>
<exception>
<functional>
C++11 <initializer_list>
<iterator>
<limits>
<locale>
<memory>
<new>
<numeric>
C++11 <random>
C++11 <ratio>
C++11 <regex>
<stdexcept>
<string>
C++11 <system_error>
C++11 <tuple>
C++11 <type_traits>
C++11 <typeindex>
<typeinfo>
<utility>
<valarray>
vector<bool>
vector::~vector
vector::vector

member functions

vector::assign
vector::back
vector::begin
vector::capacity
C++11 vector::cbegin
C++11 vector::cend
vector::clear
C++11 vector::crbegin
C++11 vector::crend
C++11 vector::data
C++11 vector::emplace
C++11 vector::emplace_back
vector::empty
vector::end
vector::erase
vector::front
vector::get_allocator
vector::insert
vector::max_size
vector::operator[]
vector::operator=
vector::pop_back
vector::push_back
vector::rbegin
vector::rend
vector::reserve
vector::resize
C++11 vector::shrink_to_fit
vector::size
vector::swap

non-member overloads

relational operators (vector)
swap (vector)

std:: vector ::rbegin

Return value.

main () { std::vector< > myvector (5); i=0; std::vector< >::reverse_iterator rit = myvector.rbegin(); (; rit!= myvector.rend(); ++rit) *rit = ++i; std::cout << ; (std::vector< >::iterator it = myvector.begin(); it != myvector.end(); ++it) std::cout << << *it; std::cout << ; 0; }

Iterator validity

Exception safety.

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vector class

9 contributors

The C++ Standard Library vector class is a class template for sequence containers. A vector stores elements of a given type in a linear arrangement, and allows fast random access to any element. A vector is the preferred container for a sequence when random-access performance is at a premium.

Type The element data type to be stored in the vector

Allocator The type that represents the stored allocator object that encapsulates details about the vector's allocation and deallocation of memory. This argument is optional and the default value is allocator<Type> .

Vectors allow constant time insertions and deletions at the end of the sequence. Inserting or deleting elements in the middle of a vector requires linear time. The deque class container is faster at insertions and deletions at the beginning and end of a sequence. The list class container is faster at insertions and deletions at any location within a sequence.

Vector reallocation occurs when a member function must increase the sequence contained in the vector object beyond its current storage capacity. Other insertions and erasures may alter various storage addresses within the sequence. In all such cases, iterators or references that point at altered portions of the sequence become invalid. If no reallocation happens, only iterators and references before the insertion/deletion point remain valid.

The vector<bool> class is a full specialization of the class template vector for elements of type bool . It has an allocator for the underlying type used by the specialization.

The vector<bool> reference class is a nested class whose objects can provide references to elements (single bits) within a vector<bool> object.

Constructors

Name	Description
	Constructs a vector of a specific size or with elements of a specific value or with a specific or as a copy of some other vector.

Name	Description
(#allocator_type)	A type that represents the class for the vector object.
	A type that provides a random-access iterator that can read a element in a vector.
	A type that provides a pointer to a element in a vector.
	A type that provides a reference to a element stored in a vector. It's used for reading and doing operations.
	A type that provides a random-access iterator that can read any element in the vector.
	A type that provides the difference between the addresses of two elements in a vector.
	A type that provides a random-access iterator that can read or modify any element in a vector.
	A type that provides a pointer to an element in a vector.
	A type that provides a reference to an element stored in a vector.
	A type that provides a random-access iterator that can read or modify any element in a reversed vector.
	A type that counts the number of elements in a vector.
	A type that represents the data type stored in a vector.

Name	Description
	Erases a vector and copies the specified elements to the empty vector.
	Returns a reference to the element at a specified location in the vector.
	Returns a reference to the last element of the vector.
	Returns a random-access iterator to the first element in the vector.
	Returns the number of elements that the vector could contain without allocating more storage.
	Returns a random-access const iterator to the first element in the vector.
	Returns a random-access const iterator that points just beyond the end of the vector.
	Returns a const iterator to the first element in a reversed vector.
	Returns a const iterator to the end of a reversed vector.
	Erases the elements of the vector.
	Returns a pointer to the first element in the vector.
	Inserts an element constructed in place into the vector at a specified position.
	Adds an element constructed in place to the end of the vector.
	Tests if the vector container is empty.
	Returns a random-access iterator that points to the end of the vector.
	Removes an element or a range of elements in a vector from specified positions.
	Returns a reference to the first element in a vector.
	Returns an object to the class used by a vector.
	Inserts an element or many elements into the vector at a specified position.
	Returns the maximum length of the vector.
	Deletes the element at the end of the vector.
	Add an element to the end of the vector.
	Returns an iterator to the first element in a reversed vector.
	Returns an iterator to the end of a reversed vector.
	Reserves a minimum length of storage for a vector object.
	Specifies a new size for a vector.
	Discards excess capacity.
	Returns the number of elements in the vector.
	Exchanges the elements of two vectors.

Name	Description
	Returns a reference to the vector element at a specified position.
	Replaces the elements of the vector with a copy of another vector.

allocator_type

A type that represents the allocator class for the vector object.

allocator_type is a synonym for the template parameter Allocator .

See the example for get_allocator for an example that uses allocator_type .

Erases a vector and copies the specified elements to the empty vector.

first Position of the first element in the range of elements to be copied.

last Position of the first element beyond the range of elements to be copied.

count The number of copies of an element being inserted into the vector.

value The value of the element being inserted into the vector.

init_list The initializer_list containing the elements to insert.

First, assign erases any existing elements in a vector. Then, assign either inserts a specified range of elements from the original vector into a vector, or it inserts copies of a new specified value element into a vector.

Returns a reference to the element at a specified location in the vector.

position The subscript or position number of the element to reference in the vector.

Return value

A reference to the element subscripted in the argument. If position is greater than the size of the vector, at throws an exception.

If the return value of at is assigned to a const_reference , the vector object can't be modified. If the return value of at is assigned to a reference , the vector object can be modified.

Returns a reference to the last element of the vector.

The last element of the vector. If the vector is empty, the return value is undefined.

If the return value of back is assigned to a const_reference , the vector object can't be modified. If the return value of back is assigned to a reference , the vector object can be modified.

When compiled by using _ITERATOR_DEBUG_LEVEL defined as 1 or 2, a runtime error occurs if you attempt to access an element in an empty vector. For more information, see Checked iterators .

Returns a random-access iterator to the first element in the vector.

A random-access iterator addressing the first element in the vector or to the location succeeding an empty vector . Always compare the value returned with vector::end to ensure it's valid.

If the return value of begin is assigned to a vector::const_iterator , the vector object can't be modified. If the return value of begin is assigned to an vector::iterator , the vector object can be modified.

Returns the number of elements that the vector could contain without allocating more storage.

The current length of storage allocated for the vector.

The member function resize will be more efficient if sufficient memory is allocated to accommodate it. Use the member function reserve to specify the amount of memory allocated.

Returns a const iterator that addresses the first element in the range.

A const random-access iterator that points at the first element of the range, or the location just beyond the end of an empty range (for an empty range, cbegin() == cend() ).

With the return value of cbegin , the elements in the range can't be modified.

You can use this member function in place of the begin() member function to guarantee that the return value is const_iterator . Typically, it's used in with the auto type deduction keyword, as shown in the following example. In the example, consider Container to be a modifiable (non- const ) container of any kind that supports begin() and cbegin() .

Returns a const past-the-end iterator that points to the element following the last element of the vector.

A const past-the-end iterator for the vector. It points to the element following the last element of the vector. That element is a placeholder and shouldn't be dereferenced. Only use it for comparisons. If the vector is empty, then vector::cend() == vector::cbegin() .

cend is used to test whether an iterator has passed the end of its range.

You can use this member function in place of the end() member function to guarantee that the return value is const_iterator . Typically, it's used with the auto type deduction keyword, as shown in the following example. In the example, consider Container to be a modifiable (non- const ) container of any kind that supports end() and cend() .

The value returned by cend shouldn't be dereferenced. Only use it for comparisons.

Erases the elements of the vector.

const_iterator

A type that provides a random-access iterator that can read a const element in a vector.

A type const_iterator can't be used to modify the value of an element.

See the example for back for an example that uses const_iterator .

const_pointer

A type that provides a pointer to a const element in a vector.

A type const_pointer can't be used to modify the value of an element.

An iterator is more commonly used to access a vector element.

const_reference

A type that provides a reference to a const element stored in a vector. It's used for reading and doing const operations.

A type const_reference can't be used to modify the value of an element.

const_reverse_iterator

A type that provides a random-access iterator that can read any const element in the vector.

A type const_reverse_iterator can't modify the value of an element and is used to iterate through the vector in reverse.

See rbegin for an example of how to declare and use an iterator.

Returns a const iterator to the first element in a reversed vector.

A const reverse random-access iterator addressing the first element in a reversed vector or addressing what had been the last element in the unreversed vector .

With the return value of crbegin , the vector object can't be modified.

Returns a const past-the-end reverse iterator that points to the element following the last element of the reversed vector.

A const reverse past-the-end iterator for the reversed vector. It points to the element following the last element of the reversed vector, which is the same as the element before the first element of the non-reversed vector. That element is a placeholder and shouldn't be dereferenced. Only use it for comparisons.

crend is used with a reversed vector just as vector::cend is used with a vector .

With the return value of crend (suitably decremented), the vector object can't be modified.

crend can be used to test to whether a reverse iterator has reached the end of its vector .

The value returned by crend shouldn't be dereferenced. Only use it for comparisons.

Returns a pointer to the first element in the vector.

A pointer to the first element in the vector or to the location succeeding an empty vector .

difference_type

A type that provides the difference between two iterators that refer to elements within the same vector.

A difference_type can also be described as the number of elements between two pointers, because a pointer to an element contains its address.

Inserts an element constructed in place into the vector at a specified position.

position The position in the vector where the first element is inserted.

args Constructor arguments. The function infers which constructor overload to invoke based on the arguments provided.

The function returns an iterator that points to the position where the new element was inserted into the vector .

Any insertion operation can be expensive, see vector class for a discussion of vector performance.

emplace_back

Adds an element constructed in place to the end of the vector.

Tests if the vector is empty.

true if the vector is empty; false if the vector isn't empty.

Returns a past-the-end iterator that points to the element following the last element of the vector.

A past-the-end iterator for the vector. It points to the element following the last element of the vector. That element is a placeholder and shouldn't be dereferenced. Only use it for comparisons. If the vector is empty, then vector::end() == vector::begin() .

If the return value of end is assigned to a variable of type const_iterator , the vector object can't be modified. If the return value of end is assigned to a variable of type iterator , the vector object can be modified.

Removes an element or a range of elements in a vector from specified positions.

position Position of the element to be removed from the vector.

first Position of the first element removed from the vector.

last Position just beyond the last element removed from the vector.

An iterator that designates the first element remaining beyond any elements removed, or a pointer to the end of the vector if no such element exists.

Returns a reference to the first element in a vector.

A reference to the first element in the vector object. If the vector is empty, the return is undefined.

If the return value of front is assigned to a const_reference , the vector object can't be modified. If the return value of front is assigned to a reference , the vector object can be modified.

get_allocator

Returns a copy of the allocator object used to construct the vector.

The allocator used by the vector.

Allocators for the vector class specify how the class manages storage. The default allocators supplied with C++ Standard Library container classes are sufficient for most programming needs. Writing and using your own allocator class is an advanced C++ feature.

Inserts an element, or many elements, or a range of elements into the vector at a specified position.

count The number of elements being inserted into the vector.

first The position of the first element in the range of elements to be copied.

last The position of the first element beyond the range of elements to be copied.

The first two insert functions return an iterator that points to the position where the new element was inserted into the vector.

As a precondition, first and last must not be iterators into the vector, or the behavior is undefined. Any insertion operation can be expensive, see vector class for a discussion of vector performance.

A type that provides a random-access iterator that can read or modify any element in a vector.

A type iterator can be used to modify the value of an element.

See the example for begin .

Returns the maximum length of the vector.

The maximum possible length of the vector.

Returns a reference to the vector element at a specified position.

position The position of the vector element.

If the position specified is greater than or equal to the size of the container, the result is undefined.

If the return value of operator[] is assigned to a const_reference , the vector object can't be modified. If the return value of operator[] is assigned to a reference, the vector object can be modified.

When compiled by using _ITERATOR_DEBUG_LEVEL defined as 1 or 2, a runtime error occurs if you attempt to access an element outside the bounds of the vector. For more information, see Checked iterators .

Replaces the elements of the vector with a copy of another vector.

right The vector being copied into the vector .

After erasing any existing elements in a vector , operator= either copies or moves the contents of right into the vector .

A type that provides a pointer to an element in a vector.

A type pointer can be used to modify the value of an element.

Deletes the element at the end of the vector.

For a code example, see vector::push_back() .

Adds an element to the end of the vector.

value The value to assign to the element added to the end of the vector.

Returns an iterator to the first element in a reversed vector.

A reverse random-access iterator addressing the first element in a reversed vector or addressing what had been the last element in the unreversed vector.

If the return value of rbegin is assigned to a const_reverse_iterator , the vector object can't be modified. If the return value of rbegin is assigned to a reverse_iterator , the vector object can be modified.

A type that provides a reference to an element stored in a vector.

See at for an example of how to use reference in the vector class.

Returns a past-the-end reverse iterator that points to the element following the last element of the reversed vector.

A reverse past-the-end iterator for the reversed vector. It points to the element following the last element of the reversed vector, which is the same as the element before the first element of the non-reversed vector. That element is a placeholder and shouldn't be dereferenced. Only use it for comparisons.

rend is used with a reversed vector just as end is used with a vector.

If the return value of rend is assigned to a const_reverse_iterator , then the vector object can't be modified. If the return value of rend is assigned to a reverse_iterator , then the vector object can be modified.

rend can be used to test to whether a reverse iterator has reached the end of its vector.

The value returned by rend shouldn't be dereferenced. Only use it for comparisons.

Reserves a minimum length of storage for a vector object, allocating space if necessary.

count The minimum length of storage to be allocated for the vector.

Specifies a new size for a vector.

new_size The new size of the vector.

value The initialization value of new elements added to the vector if the new size is larger that the original size. If the value is omitted, the new objects use their default constructor.

If the container's size is less than the requested size, new_size , resize adds elements to the vector until it reaches the requested size. When the container's size is larger than the requested size, resize deletes the elements closest to the end of the container until it reaches the size new_size . No action is taken if the present size of the container is the same as the requested size.

size reflects the current size of the vector.

reverse_iterator

A type that provides a random-access iterator that can read or modify any element in a reversed vector.

A type reverse_iterator is used to iterate through the vector in reverse.

See the example for rbegin .

shrink_to_fit

Discards excess capacity.

Returns the number of elements in the vector.

The current length of the vector.

A type that counts the number of elements in a vector.

See the example for capacity .

Exchanges the elements of two vectors.

right A vector providing the elements to be swapped. Or, a vector whose elements are to be exchanged with the elements in the vector left .

left A vector whose elements are to be exchanged with the elements in the vector right .

A type that represents the data type stored in a vector.

value_type is a synonym for the template parameter Type .

Constructs a vector. Overloads construct a vector of a specific size, or with elements of a specific value. Or, as a copy of all or part of some other vector. Some overloads also allow you to specify the allocator to use.

allocator The allocator class to use with this object. get_allocator returns the allocator class for the object.

count The number of elements in the constructed vector.

value The value of the elements in the constructed vector.

source The vector of which the constructed vector is to be a copy.

init_list The initializer_list containing the elements to copy.

All constructors store an allocator object ( allocator ) and initialize the vector.

The first two constructors specify an empty initial vector. The second constructor explicitly specifies the allocator type ( allocator ) to use.

The third constructor specifies a repetition of a specified number ( count ) of elements of the default value for class Type .

The fourth and fifth constructors specify a repetition of ( count ) elements of value value .

The sixth constructor specifies a copy of the vector source .

The seventh constructor moves the vector source .

The eighth constructor uses an initializer_list to specify the elements.

The ninth and tenth constructors copy the range [ first , last ) of a vector.

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COMMENTS

How can I insert element into beginning of vector?
Use the std::vector::insert function accepting an iterator to the first element as a target position (iterator before which to insert the element): #include <vector> int main () { std::vector<int> v { 1, 2, 3, 4, 5 }; v.insert (v.begin (), 6); } Alternatively, append the element and perform the rotation to the right:
std::vector<T,Allocator>::insert
std::vector Inserts elements at the specified location in the container. 1-2) inserts value before pos. 3) inserts count copies of the value before pos. 4) inserts elements from range [first, last) before pos. The behavior is undefined if first and last are iterators into *this. 5) inserts elements from initializer list ilist before pos.
c++
All overloaded versions of the method insert require that the first argument would be of type std::vector<Box>::const_iterator applied to your vector definition. This iterator specifies the position where a new element must be inserted. However you are passing in an integer value 1 instead of the iterator
std::vector<T,Allocator>::begin, std::vector<T,Allocator>::cbegin
std::vector<T,Allocator>:: cbegin. Returns an iterator to the first element of the vector. If the vector is empty, the returned iterator will be equal to end () .
::insert
Insert elements The vector is extended by inserting new elements before the element at the specified position, effectively increasing the container size by the number of elements inserted. This causes an automatic reallocation of the allocated storage space if -and only if- the new vector size surpasses the current vector capacity.
How to insert element at beginning of vector
Teams. Q&A for work. Connect and share knowledge within a single location that is structured and easy to search. Learn more about Teams
Insert or push_back to end of a std::vector?
The first method using std::vector::push_back will undergo several reallocations compared to std::vector::insert. The insert will internally allocate memory, according to the current std::vector::capacity before copying the range. See the following discussion for more: Does std::vector::insert reserve by definition?
How to append or insert std::array elements into a std::vector?
There is not much to add here when talking about insertion into the middle - the only notable difference is that it will always be less efficient, as the remaining elements in the destination std::vector will be move-constructed (which is O (N)).
std::vector
1)std::vectoris a sequence container that encapsulates dynamic size arrays. 2)std::pmr::vectoris an alias template that uses a polymorphic allocator. The elements are stored contiguously, which means that elements can be accessed not only through iterators, but also using offsets to regular pointers to elements.
Insert an element at the beginning of a vector in C++
This post will discuss how to insert an element at the beginning of a vector in C++. 1. Using std::vector::insert function The standard solution to insert an element to a vector is with the std::vector::insert function. It takes an iterator to the position where the element needs to be inserted.
vector::begin() and vector::end() in C++ STL
begin () function is used to return an iterator pointing to the first element of the vector container. begin () function returns a bidirectional iterator to the first element of the container. Syntax : vectorname.begin () Parameters: No parameters are passed. Return Type: This function returns a bidirectional iterator pointing to the first element.
C++ Tutorial: A Beginner's Guide to std::vector, Part 1
The first step using vector is to include the appropriate header: #include <vector> Note that the header file name does not have any extension; this is true for all of the Standard Library header files. The second thing to know is that all of the Standard Library lives in the namespace std.
vector insert() function in C++ STL
std::vector::insert () is a built-in function in C++ STL that inserts new elements before the element at the specified position, effectively increasing the container size by the number of elements inserted. Time Complexity - Linear O (N) Syntax: vector_name.insert (position, val) Parameter: The function accepts two parameters specified as below:
std::begin, std::cbegin
std:: cbegin. Returns an iterator to the beginning of the given range. 1) Returns exactly c.begin(), which is typically an iterator to the beginning of the sequence represented by c. If C is a standard Container, this returns C::iterator when c is not const-qualified, and C::const_iterator otherwise. 2) Returns a pointer to the beginning of the ...
std::inserter with set
When creating the std::inserter, out is empty so out.begin() == out.end() so I can't see it makes any difference whether I specify out.begin() or out.end() as the hint. However, if this is interpreted at inserting every element at begin() , it doesn't seem that I would get the optimum algorithmic performance.
How to insert an element of vector2 and int to a hash table?
I tried to use a different way to insert that is: m_buckets [index].push_back (make_pair (key, value) but it only gives me another error: struct std::pair<Vector2, int> has no member named push.back Vector2 is a vector class that takes to integers x and y. std::vector<std::pair<Vector2, int>> m_buckets c++ data-structures hashtable Share
C++ : How to insert element in vector at specific position
std::vector<int> vecOfNums { 1, 4, 5, 22, 33, 2, 11, 89, 49 }; Now we want to insert an element at index position 4th (In vector position index start from 0), Copy to clipboard // Create Iterator pointing to 4th Position auto itPos = vecOfNums.begin() + 4; // Insert element with value 9 at 4th Position in vector
How to Insert Several Elements in a Vector (With No Memory Errors)
To insert several individual values in order in a vector, we can use the insert interface this way: auto v = std::vector<int> {10, 20}; v.insert (begin (v) + 1, 1); v.insert (begin (v) + 2, 2); v.insert (begin (v) + 3, 3); v.insert (begin (v) + 4, 4); v.insert (begin (v) + 5, 5); If we print the collection we get this: 10 1 2 3 4 5 20
std::insert_iterator
std::insert_iterator is a LegacyOutputIterator that inserts elements into a container for which it was constructed, at the position pointed to by the supplied iterator. The container's insert () member function is called whenever the iterator (whether dereferenced or not) is assigned to. Incrementing the std::insert_iterator is a no-op.
::rbegin
Returns a reverse iterator pointing to the last element in the vector (i.e., its reverse beginning). Reverse iterators iterate backwards: increasing them moves them towards the beginning of the container. rbegin points to the element right before the one that would be pointed to by member end. Notice that unlike member vector::back, which returns a reference to this same element, this function ...
vector class
Name Description [allocator_type](#allocator_type) A type that represents the allocator class for the vector object.: const_iterator: A type that provides a random-access iterator that can read a const element in a vector.: const_pointer
C++ vector insert
The vector insert () is one of the functions from the vector package library, and it is used to calculate the insert of the user input to the vector containers. #include<iostream> #include<vector> data type main() { std :: vector < data type > object name size declaration; objectname.insert( parameters); --- some c ++ code logics --- }