std::basic_string::npos(3)

NAME
std::basic_string::npos - std::basic_string::npos

Synopsis
   static const size_type npos = -1;
   This is a special value equal to the maximum value representable by the type
   size_type. The exact meaning depends on context, but it is generally used either as
   end of string indicator by the functions that expect a string index or as the error
   indicator by the functions that return a string index.

Note
   Although the definition uses -1, size_type is an unsigned integer type, and the
   value of npos is the largest positive value it can hold, due to signed-to-unsigned
   implicit conversion. This is a portable way to specify the largest value of any
   unsigned type.

Example
// Run this code
 #include <iostream>
 #include <bitset>
 #include <string>
 int main()
 {
     // string search functions return npos if nothing is found
     std::string s = "test";
     if(s.find('a') == std::string::npos)
         std::cout << "no 'a' in 'test'\n";
     // functions that take string subsets as arguments
     // use npos as the "all the way to the end" indicator
     std::string s2(s, 2, std::string::npos);
     std::cout << s2 << '\n';
     std::bitset<5> b("aaabb", std::string::npos, 'a', 'b');
     std::cout << b << '\n';
 }

Output:
 no 'a' in 'test'
 st
 00011

See also
   npos special value. The exact meaning depends on the context
   [static] (C++17) (public static member constant of
                    std::basic_string_view<CharT,Traits>)