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std::basic_string<CharT,Traits,Allocator>::npos

From cppreference.com
< cpp‎ | string‎ | basic string
 
 
 
std::basic_string
 
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

[edit] See also

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