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Showing content from https://en.cppreference.com/w/cpp/language/../algorithm/../../cpp/container/list/front.html below:

std::list<T,Allocator>::front - cppreference.com

reference front();

(1) (constexpr since C++26)

const_reference front() const;

(2) (constexpr since C++26)

Returns a reference to the first element in 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 âobserveâ evaluation semantic, the behavior is undefined.
If the implementation is not hardened, the behavior is undefined.

(since C++26) [edit] Return value

Reference to the first element.

[edit] Complexity

Constant.

[edit] Notes

For a container c, the expression c.front() is equivalent to *c.begin().

[edit] Example

The following code uses front to display the first element of a std::list<char>:

#include <cassert>
#include <list>
 
int main()
{
    std::list<char> letters{'a', 'b', 'c', 'd'};
    assert(letters.front() == 'a');
}

[edit] See also access the last element
(public member function) [edit] returns a reverse iterator to the end
(public member function) [edit] returns an iterator to the beginning
(public member function) [edit]

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