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Difference between revisions of "cpp/container/vector/assign"

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Revision as of 16:55, 2 November 2012

[edit template]
 
C++
 
Containers library
 
std::vector
Member types
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) (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)
3) Replaces the contents with the elements from ilist.

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

Contents

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::vector<char>:

Run this code
#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

See also

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