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

	(1)
`basic_string substr( size_type pos = 0, size_type count = npos ) const;`			( C++20)
`constexpr basic_string substr( size_type pos = 0, size_type count = npos ) const;`			( C++20) ( C++23)
`constexpr basic_string substr( size_type pos = 0, size_type count = npos ) const&;`			( C++23)
`constexpr basic_string substr( size_type pos = 0, size_type count = npos ) &&;`		(2)	( C++23)

[pos, pos + count). , .. count , size() - pos (, count == npos), [pos, size()).

1) return basic_string(*this, pos, count);.

2) return basic_string(std::move(*this), pos, count);.

pos		,
count

, [pos, pos + count) [pos, size()).

std::out_of_range, pos > size().

- , ( ).

count.

: get_allocator().

#include <iostream>
#include <string>
 
int main()
{
    std::string a = "0123456789abcdefghij";
 
    // count  npos,  [pos, size())
    std::string sub1 = a.substr(10);
    std::cout << sub1 << '\n';
    
    //  pos,  pos + count    ,  [pos, pos + count)
    std::string sub2 = a.substr(5, 3);
    std::cout << sub2 << '\n';
    
    // pos    , pos + count ,  [pos, size())
    std::string sub4 = a.substr(a.size() - 3, 50);
    //   
    // std::string sub4 = a.substr(17, 3);
    //  a.size() == 20, pos == a.size() - 3 == 17,  a.size() - pos == 3
    
    std::cout << sub4 << '\n';

    try
    {
        // pos    ,  
        std::string sub5 = a.substr(a.size() + 3, 50);
        std::cout << sub5 << '\n';
    }
    catch (const std::out_of_range& ex)
    {
        std::cout << ex.what() << '\n';
    }
}

:

abcdefghij
567
hij
basic_string::substr: __pos (which is 23) > this->size() (which is 20)

C++:


LWG 847	C++98

copy	(public -) []
sizelength	(public -) []
find	(public -) []
npos [static]	. (public static -) []
substr (C++17)	(public - `std::basic_string_view<CharT,Traits>`) []







(C++20)

(C++20)
(C++11)





(C++20)


/

(C++11)
(C++11)
(C++11)
(C++17)

cppreference.com

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