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

 

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std::forward_list

Member functions
forward_list::forward_list forward_list::~forward_list forward_list::operator= forward_list::assign forward_list::assign_range (C++23)   forward_list::get_allocator Element access forward_list::front Iterators forward_list::before_beginforward_list::cbefore_begin forward_list::beginforward_list::cbegin forward_list::endforward_list::cend Capacity forward_list::empty forward_list::max_size	Modifiers forward_list::clear forward_list::emplace_front forward_list::push_front forward_list::insert_after forward_list::emplace_after forward_list::erase_after forward_list::insert_range_after (C++23) forward_list::prepend_range (C++23) forward_list::pop_front forward_list::resize forward_list::swap Operations forward_list::merge forward_list::splice_after forward_list::removeforward_list::remove_if forward_list::reverse forward_list::unique forward_list::sort
Non-member functions
operator==operator<=> (C++20) swap(std::forward_list) erase(std::forward_list)erase_if(std::forward_list) (C++20)(C++20)	operator!=operator<operator>operator<=operator>= (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)
Deduction guides (C++17)

 

void resize( size_type count );	(1)	(since C++11) (constexpr since C++26)
void resize( size_type count, const value_type& value );	(2)	(since C++11) (constexpr since C++26)

Resizes the container to contain count elements:

• If count is equal to the current size, does nothing.
• 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, then:

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
- If the following condition is satisfied, the behavior is undefined: 1) T is not DefaultInsertable into forward_list. 2) T is not CopyInsertable into forward_list.

Complexity

Linear in the difference between the current size and count. Additional complexity possible due to list traversal to reach the first element to erase/the end position to insert.

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 <forward_list>
#include <iostream>
 
void print(auto rem, const std::forward_list<int>& c)
{
    for (std::cout << rem; const int el : c)
        std::cout << el << ' ';
    std::cout << '\n';
}
 
int main()
{
    std::forward_list<int> c = {1, 2, 3};
    print("The forward_list 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 forward_list 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

See also

max_size	returns the maximum possible number of elements (public member function)
empty	checks whether the container is empty (public member function)