std::vector<T,Allocator>::assign

void assign( size_type count, const T& value );	(1)	(constexpr since C++20)
template< class InputIt > void assign( InputIt first, InputIt last );	(2)	(constexpr since C++20)
void assign( std::initializer_list<T> ilist );	(3)	(since C++11) (constexpr since C++20)

Replaces the contents of the container.

1) Replaces the contents with count copies of value value.

2) Replaces the contents with copies of those in the range [first, last).

If either argument is an iterator into *this, the behavior is undefined.

This overload has the same effect as overload (1) if `InputIt` is an integral type.	(until C++11)
This overload participates in overload resolution only if `InputIt` satisfies LegacyInputIterator.	(since C++11)

Each iterator in the range [first, last) is dereferenced exactly once.

3) Replaces the contents with the elements from ilist.

All iterators (including the end() iterator) and all references to the elements are invalidated.

Parameters

count	-	the new size of the container
value	-	the value to initialize elements of the container with
first, last	-	the pair of iterators defining the source range of elements to copy
ilist	-	the initializer list to copy the values from

Complexity

1) Linear in count.

2) Linear in distance between first and last.

3) Linear in ilist.size().

Example

The following code uses assign to add several characters to a std::vector<char>:

#include <vector>
#include <iostream>
#include <string>

int main()
{
    std::vector<char> characters;
    
    auto print_vector = [&]()
    {
        for (char c : characters)
            std::cout << c << ' ';
        std::cout << '\n';
    };
    
    characters.assign(5, 'a');
    print_vector();
    
    const std::string extra(6, 'b');
    characters.assign(extra.begin(), extra.end());
    print_vector();
    
    characters.assign({'C', '+', '+', '1', '1'});
    print_vector();
}

Output:

a a a a a
b b b b b b
C + + 1 1

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 2209	C++98	the replacement operation was required to be implemented as erasing all existing elements followed by inserting the given elements	removed the requirement

assign_range (C++23)	assigns a range of values to the container (public member function)
operator=	assigns values to the container (public member function)

std::vector<T,Allocator>::assign

Parameters

Complexity

Example

Defect reports

See also