std::forward_list resize() method

since C++11

// (1) Non const version only
void resize( size_type count );

// (2) Non const version only
void resize( size_type count, const value_type& value );

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

• (1) - T (the container's element type) must meet the requirements of DefaultInsertable.
• (2) - T (the container's element type) must meet the requirements of CopyInsertable.

Return value

(none)

Complexity

Linear in the difference between the current size and count - O(size() - count).

important

Additional complexity possible due to list traversal to reach the first element to erase/the end position to insert.

Exceptions

(none)

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

Main.cpp

#include <iostream>
#include <forward_list>

int main()
{
    std::forward_list<int> c = {1, 2, 3};
    std::cout << "The forward_list 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 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