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

From cppreference.net
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

Return value

operator [ ] ( 0 )

Complexity

Constant.

Notes

In libstdc++, front() is not available in C++98 mode.

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

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

See also

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