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std::deque<T,Allocator>::front

From cppreference.com
< cpp‎ | container‎ | deque
 
 
 
std::deque
(until C++20)(until C++20)(until C++20)(until C++20)(until C++20)
 
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 "observe" 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::deque <char>:

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

[edit] See also

access the last element
(public member function) [edit]
(C++11)
returns a reverse iterator to the end
(public member function) [edit]
(C++11)
returns an iterator to the beginning
(public member function) [edit]
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