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

void resize( size_type count );	(1)	(since C++11)
	(2)
void resize( size_type count, T value = T() );			(until C++11)
void resize( size_type count, const value_type& value );			(since C++11)

Resizes the container to contain count elements.

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

Language
Standard Library Headers
Freestanding and hosted implementations
Named requirements
Language support library
Concepts library (C++20)
Diagnostics library
Utilities library
Strings library
Containers library
Iterators library
Ranges library (C++20)
Algorithms library
Numerics library
Localizations library
Input/output library
Filesystem library (C++17)
Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)
Technical Specifications

array (C++11)
vector
deque
forward_list (C++11)
list
set
multiset
map
multimap
unordered_set (C++11)
unordered_multiset (C++11)
unordered_map (C++11)
unordered_multimap (C++11)
stack
queue
priority_queue
span (C++20)

Member functions
deque::deque
deque::~deque
deque::operator=
deque::assign
deque::get_allocator
Element access
deque::at
deque::operator[]
deque::front
deque::back
Iterators
deque::begindeque::cbegin (C++11)
deque::enddeque::cend (C++11)
deque::rbegindeque::crbegin (C++11)
deque::renddeque::crend (C++11)
Capacity
deque::empty
deque::size
deque::max_size
deque::shrink_to_fit
Modifiers
deque::clear
deque::insert
deque::emplace
deque::erase
deque::push_front
deque::emplace_front
deque::pop_front
deque::push_back
deque::emplace_back
deque::pop_back
deque::resize
deque::swap
Non-member functions
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)

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