std::basic_string_view::npos(3)

NAME
std::basic_string_view::npos - std::basic_string_view::npos

Synopsis
   static constexpr size_type npos = size_type(-1); (since C++17)
   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 view indicator by the functions that expect a view index or as the error
   indicator by the functions that return a view index.

Example
// Run this code
 #include <string_view>
 constexpr bool
 contains(std::string_view const what, std::string_view const where) noexcept {
     return std::string_view::npos != where.find(what);
 }
 int main()
 {
     using namespace std::literals;
     static_assert(contains("water", "in a bottle of water"));
     static_assert(!contains("wine", "in a bottle of champagne"));
     static_assert(""sv.npos == "haystack"sv.find("needle"));
 }

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