std::string_view substr() method

since C++17

// Const version onlyconstexpr 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

ABCDEFBCDEFCDEEFbasic_string_view::substr: __pos (which is 666) > __size (which is 6)