std::basic_string<CharT,Traits,Allocator>::npos - cppreference.com (original) (raw)

| 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.

[edit] 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.

[edit] Example

#include #include #include   int main() { // string search functions return npos if nothing is found std::string s = "test"; if (s.find('a') == s.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:🧵:npos); std::cout << s2 << '\n';   std::bitset<5> b("aaabb", std:🧵:npos, 'a', 'b'); std::cout << b << '\n'; }

Output:

no 'a' in 'test' st 00011

[edit] See also

| | special value. The exact meaning depends on the context (public static member constant of std::basic_string_view<CharT,Traits>) [edit] | | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |