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std::basic_string<CharT,Traits,Allocator>::front

From cppreference.com
< cpp‎ | string‎ | basic string
 
C++
 
Strings library
 
std::basic_string
 
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)

Contents

[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

[edit] See also

(DR*)
 accesses the last character
(public member function) [edit]
accesses the first character
(public member function of std::basic_string_view<CharT,Traits>) [edit]
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