std::basic_string<CharT,Traits,Allocator>::front - cppreference.com (original) (raw)
| 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. | (since C++26) |
[edit] Return value
operator[](0)
[edit] Complexity
Constant.
[edit] Notes
In libstdc++, front() is not available in C++98 mode.
[edit] Example
#include #include 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:
[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 |
[edit] See also
| | accesses the last character (public member function) [edit] | | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | | accesses the first character (public member function of std::basic_string_view<CharT,Traits>) [edit] |