std::deque<T,Allocator>::front
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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.
Contents
[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'); }