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

From cppreference.net

C++
Containers library
std::forward_list
Member functions
Non-member functions
(until C++20) (until C++20) (until C++20) (until C++20) (until C++20)
Deduction guides (C++17)
void pop_front ( ) ;
(since C++11)
(constexpr since C++26)

Removes the first element of the container.

If empty() is true , the behavior is undefined.

(until C++26)

If empty() is true :

  • If the implementation is hardened , a contract violation occurs. Moreover, if the contract-violation handler returns under “observe” evaluation semantic, the behavior is undefined.
  • If the implementation is not hardened, the behavior is undefined.
(since C++26)

References and iterators to the erased element are invalidated.

Complexity

Constant.

Example

Run this code 
#include <forward_list>
#include <iostream>
int main()
{
    std::forward_list<char> chars{'A', 'B', 'C', 'D'};
    for (; !chars.empty(); chars.pop_front())
        std::cout << "chars.front(): '" << chars.front() << "'\n";
}

Output: 

chars.front(): 'A'
chars.front(): 'B'
chars.front(): 'C'
chars.front(): 'D'

See also

inserts an element to the beginning
(public member function)
access the first element
(public member function)