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std::deque<T,Allocator>::resize

void resize( size_type count );
(1)
void resize( size_type count, const value_type& value );
(2)

Resizes the container to contain count elements, does nothing if count == size().

If the current size is greater than count, the container is reduced to its first count elements.

If the current size is less than count,

1) additional default-inserted elements are appended
2) additional copies of value are appended.

Parameters

count - new size of the container
value - the value to initialize the new elements with
Type requirements
-T must meet the requirements of MoveInsertable and DefaultInsertable in order to use overload (1).
-T must meet the requirements of CopyInsertable in order to use overload (2).

Return value

(none).

Complexity

Linear in the difference between the current size and count.

Notes

If value-initialization in overload (1) is undesirable, for example, if the elements are of non-class type and zeroing out is not needed, it can be avoided by providing a custom Allocator::construct.

Example

#include <iostream>
#include <deque>
 
int main()
{
    std::deque<int> c = {1, 2, 3};
    std::cout << "The deque holds: ";
    for (const auto& el: c)
        std::cout << el << ' ';
    std::cout << '\n';
 
    c.resize(5);
    std::cout << "After resize up to 5: ";
    for (const auto& el: c)
        std::cout << el << ' ';
    std::cout << '\n';
 
    c.resize(2);
    std::cout << "After resize down to 2: ";
    for (const auto& el: c)
        std::cout << el << ' ';
    std::cout << '\n';
 
    c.resize(6, 4);
    std::cout << "After resize up to 6 (initializer = 4): ";
    for (const auto& el: c)
        std::cout << el << ' ';
    std::cout << '\n';
}

Output:

The deque holds: 1 2 3
After resize up to 5: 1 2 3 0 0
After resize down to 2: 1 2
After resize up to 6 (initializer = 4): 1 2 4 4 4 4

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 679 C++98 resize() passed value by value passes by const reference
LWG 1418 C++98 the behavior of resize(size()) was not specified specified

See also

returns the number of elements
(public member function)
inserts elements
(public member function)
erases elements
(public member function)

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