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staticconst size_type npos=-1; | ||
This is a special value equal to the maximum value representable by the typesize_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.
Although the definition uses-1,size_type is an unsigned integer type, and the value ofnpos is the largest positive value it can hold, due tosigned-to-unsigned implicit conversion. This is a portable way to specify the largest value of any unsigned type.
#include <bitset>#include <iostream>#include <string> int main(){// string search functions return npos if nothing is foundstd::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" indicatorstd::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'st00011
[static] | special value. The exact meaning depends on the context (public static member constant of std::basic_string_view<CharT,Traits>)[edit] |
