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std::basic_string::substr(3)  C++ Standard Libary std::basic_string::substr(3)

NAME
       std::basic_string::substr - std::basic_string::substr

Synopsis
	  basic_string	substr(	 size_type  pos	 = 0, size_type	count =	npos )
       (until C++20)
	  const;
	  constexpr basic_string substr( size_type pos = 0, size_type count  =
       (since C++20)
	  npos ) const;

	  Returns a substring [pos, pos+count).	If the requested substring ex-
       tends past the
	  end of the string, i.e. the count is greater than size() - pos (e.g.
       if count	==
	  npos), the returned substring	is [pos, size()).

Parameters
	  pos	- position of the first	character to include
	  count	- length of the	substring

Return value
	  String containing the	substring [pos,	pos+count) or [pos, size()).

Exceptions
	  std::out_of_range if pos > size()

Complexity
	  Linear in count

Notes
	  The returned string is constructed as	if by basic_string(data()+pos,
       count), which
	  implies  that	 the  returned string's	allocator will be default-con-
       structed	 the new
	  allocator might not be a copy	of this->get_allocator().

Example
       // Run this code

	#include <string>
	#include <iostream>

	int main()
	{
	    std::string	a = "0123456789abcdefghij";

	    // count is	npos, returns [pos, size())
	    std::string	sub1 = a.substr(10);
	    std::cout << sub1 << '\n';

	    // both  pos  and  pos+count  are  within  bounds,	returns	 [pos,
       pos+count)
	    std::string	sub2 = a.substr(5, 3);
	    std::cout << sub2 << '\n';

	    // pos is within bounds, pos+count is not, returns [pos, size())
	    std::string	sub4 = a.substr(a.size()-3, 50);
	    // this is effectively equivalent to
	    // std::string sub4	= a.substr(17, 3);
	    // since a.size() == 20, pos == a.size()-3 == 17, and a.size()-pos
       == 3

	    std::cout << sub4 << '\n';

	    try	{
		// pos is out of bounds, throws
		std::string sub5 = a.substr(a.size()+3,	50);
		std::cout << sub5 << '\n';
	    } catch(const std::out_of_range& e)	{
		std::cout << "pos exceeds string size\n";
	    }
	}

Output:
	abcdefghij
	567
	hij
	pos exceeds string size

See also
	  copy	   copies characters
		   (public member function)
	  size	   returns the number of characters
	  length   (public member function)
	  find	   find	characters in the string
		   (public member function)
	  npos	   special value. The exact meaning depends on the context
	  [static] (public static member constant)

http://cppreference.com		  2022.07.31	  std::basic_string::substr(3)

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