std::basic_string<CharT,Traits,Allocator>::front
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std::basic_string
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(C++23)
basic_string::front
(DR*)
(DR*)
(C++23)
(DR*)
(C++23)
(C++23)
(C++20)
(C++20)
(C++23)
(C++20)(C++20)
(until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20)
(C++11)(C++11)(C++11)
(C++11)(C++11)
(C++14)
(C++11)
CharT& front();
(1)
(constexpr since C++20)
const CharT& front() const;
(2)
(constexpr since C++20)
Returns reference to the first character in the string.
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.
[edit] Return value
operator[](0)
[edit] Complexity
Constant.
[edit] Notes
In libstdc++, front() is not available in C++98 mode.
[edit] Example
Run this code
#include <iostream> #include <string> int main() { std::string s("Exemplary"); char& f1 = s.front(); f1 = 'e'; std::cout << s << '\n'; // "exemplary" std::string const c("Exemplary"); char const& f2 = c.front(); std::cout << &f2 << '\n'; // "Exemplary" }
Output:
exemplary Exemplary
[edit] Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 534 | C++98 | std::basic_string did not have the member function front()
|
added |