std::basic_string_view<CharT,Traits>:: npos

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

#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