std::string at() method

since C++20

// Non const version
constexpr reference at( size_type pos );

// Const version
constexpr const_reference at( size_type pos ) const;

until C++20

// Non const version
reference at( size_type pos );

// Const version
const_reference at( size_type pos ) const;

Returns a reference

to the character at specified index pos.

Bounds checking is performed.

Parameters

• pos - position of the character to return

Return value

Reference to the requested character.

Exceptions

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

Complexity

Constant - O(1).

Example

#include <stdexcept>
#include <iostream>
#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