NAME

std::basic_string::at - std::basic_string::at

Synopsis

CharT& at( size_type pos ); (1) (constexpr since C++20)
const CharT& at( size_type pos ) const; (2) (constexpr since C++20)

Returns a reference to the character at specified location pos. Bounds checking is
performed, exception of type std::out_of_range will be thrown on invalid access.

Parameters

pos - position of the character to return

Return value

Reference to the requested character.

Exceptions

Throws std::out_of_range if pos >= size().

If an exception is thrown for any reason, these functions have no effect (strong
exception safety guarantee).

Complexity

Constant.

Example

// Run this code

#include <iostream>
#include <stdexcept>
#include <string>

int main()
{
std::string s("message"); // for capacity

s = "abc";
s.at(2) = 'x'; // OK
std::cout << s << '\n';

std::cout << "string size = " << s.size() << '\n';
std::cout << "string capacity = " << s.capacity() << '\n';

try
{
// This will throw since the requested offset is greater than the current size.
s.at(3) = 'x';
}
catch (std::out_of_range const& exc)
{
std::cout << exc.what() << '\n';
}
}

Possible output:

abx
string size = 3
string capacity = 7
basic_string::at

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 847 C++98 there was no exception safety added strong exception safety
guarantee guarantee