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std::basic_string<CharT,Traits,Allocator>::operator[]

	(1)
reference operator[]( size_type pos );		(until C++20)
constexpr reference operator[]( size_type pos );		(since C++20)
	(2)
const_reference operator[]( size_type pos ) const;		(until C++20)
constexpr const_reference operator[]( size_type pos ) const;		(since C++20)

Returns a reference to the character at specified location pos if pos < size(), or a reference to CharT() if pos == size(). No bounds checking is performed.

If pos > size(), the behavior is undefined.

For overload (1), if pos == size(), the behavior is undefined if the object referred by the returned reference is modified to any value other than CharT() (since C++11).

Parameters

pos

position of the character to return

Return value

*(begin() + pos) if pos < size(), or a reference to CharT() if pos == size().

Complexity

Constant.

Example

#include <iostream>
#include <string>
 
int main()
{
    const std::string e("Exemplar");
    for (unsigned i = e.length() - 1; i != 0; i /= 2)
        std::cout << e[i];
    std::cout << '\n';
 
    const char* c = &e[0];
    std::cout << c << '\n'; // print as a C string
 
    // Change the last character of s into a 'y'
    std::string s("Exemplar ");
    s[s.size() - 1] = 'y'; // equivalent to s.back() = 'y';
    std::cout << s << '\n';
}

Output:

rmx
Exemplar
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 259	C++98	`data()[pos]` was returned if `pos < size()` (its type is `const CharT&`, which conflicts with `reference`)	changed to `*(begin() + pos)`
LWG 2475	C++11	if `pos == size()`, the behavior of modifying the object referred by the returned reference was undefined	well-defined if modified to `CharT()`

at	accesses the specified character with bounds checking (public member function)
front (DR*)	accesses the first character (public member function)
back (DR*)	accesses the last character (public member function)
operator[] (C++17)	accesses the specified character (public member function of `std::basic_string_view<CharT,Traits>`)