std::forward_list::resize(3)

NAME
std::forward_list::resize - std::forward_list::resize

Synopsis
   void resize( size_type count ); (1) (since C++11)
   void resize( size_type count, const value_type& value ); (2) (since C++11)
   Resizes the container to contain count elements, does nothing if count ==
   std::distance(begin(), end()) (i.e. if count is equal to the current 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 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. 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
   insert_after inserts elements after an element
                (public member function)
   erase_after erases an element after an element
                (public member function)