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

 

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std::swap

eraseerase_if (C++20)(C++20)

operator==operator!=operator<operator>operator<=operator>=operator<=> (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20)

Deduction guides(C++17)

 

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

Run this code

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

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

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