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

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C++
Containers library
std::list
Member functions
Non-member functions
(until C++20) (until C++20) (until C++20) (until C++20) (until C++20)
Deduction guides (C++17)
void assign ( size_type count, const T & value ) ;
(1)
template < class InputIt >
void assign ( InputIt first, InputIt last ) ;
(2)
void assign ( std:: initializer_list < T > ilist ) ;
(3) (since C++11)

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)
3) Replaces the contents with the elements from ilist .

All iterators, pointers and references to the elements of the container are invalidated.

Parameters

count - the new size of the container
value - the value to initialize elements of the container with
first, last - the range to copy the elements from
ilist - std::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:: list < char > :

Run this code 
#include <list>
#include <iostream>
#include <string>
 
int main()
{
    std::list<char> characters;
 
    auto print_list = [&]()
    {
        for (char c : characters)
            std::cout << c << ' ';
        std::cout << '\n';
    };
 
    characters.assign(5, 'a');
    print_list();
 
    const std::string extra(6, 'b');
    characters.assign(extra.begin(), extra.end());
    print_list();
 
    characters.assign({'C', '+', '+', '1', '1'});
    print_list();
}

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 320 C++98 the replacement operation was required to be implemented as
erasing all existing elements followed by inserting the given elements 		removed the
requirement

See also

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