std::basic_string<CharT,Traits,Allocator>::front - cppreference.com

From cppreference.com

	(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.
If the implementation is not hardened, the behavior is undefined.

(since C++26)

Return value

operator[](0)

Complexity

Constant.

Notes

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

Example

#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:

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