NAME¶

std::deque::resize - std::deque::resize

Synopsis¶

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
1. elements were removed by using
LWG 2033 C++11 erase() 1. uses pop_back()
2. T was not required to be 2. required
MoveInsertable

See also¶

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