std::string_view substr() method

since C++17

// Const version only
constexpr basic_string substr( size_type pos = 0, size_type count = npos ) const;

Returns a view of the substring [ pos, pos + rcount ), where rcount is std::min(count, size() - pos).

Parameters

• pos - position of the first character
• count - requested length

Return value

View of the substring [ pos, pos + rcount ).

Complexity

Constant - O(1).

Exceptions

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

Example

#include <cstddef>
#include <iostream>
#include <stdexcept>
#include <string_view>
 
int main()
{
    typedef std::size_t count_t, pos_t;
 
    constexpr std::string_view data{"ABCDEF"};
 
    std::cout << data.substr() << '\n'; // ABCDEF
    std::cout << data.substr(pos_t(1)) << '\n'; // BCDEF
    std::cout << data.substr(pos_t(2), count_t(3)) << '\n'; // CDE
 
    std::cout << data.substr(pos_t(4), count_t(42)) << '\n'; // EF
        // count -> 2 == size() - pos == 6 - 4
 
    try {
        data.substr(pos_t(666), count_t(1)); // throws: pos > size()
    }
    catch(std::out_of_range const& ex) {
        std::cout << ex.what() << '\n';
    }
}

Possible output

ABCDEF
BCDEF
CDE
EF
basic_string_view::substr: __pos (which is 666) > __size (which is 6)