std::basic_string<CharT,Traits,Allocator>::npos
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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
Run this code
#include <bitset> #include <iostream> #include <string> 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::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