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std::deque<T,Allocator>::pop_front - cppreference.com

From cppreference.com

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)

Iterators and references to the erased element are invalidated. If the element is the last element in the container, the end() iterator is also invalidated. Other references and iterators are not affected.

Complexity

Constant.

Example

#include <deque>
#include <iostream>

int main()
{
    std::deque<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

removes the last element
(public member function) [edit]
inserts an element to the beginning
(public member function) [edit]
access the first element
(public member function) [edit]