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

< cpp‎ | string‎ | basic string

reference at( size_type pos );		(until C++20)
constexpr reference at( size_type pos );		(since C++20)
const_reference at( size_type pos ) const;		(until C++20)
constexpr const_reference at( size_type pos ) const;		(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().

Complexity

Constant.

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