NAME¶

std::basic_string::npos - std::basic_string::npos

Synopsis¶

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.

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.

Example¶

// Run this code

#include <iostream>
#include <bitset>
#include <string>

int main()
{
// string search functions return npos if nothing is found
std::string s = "test";
if(s.find('a') == std::string::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

See also¶

npos special value. The exact meaning depends on the context
[static] (C++17) (public static member constant of
std::basic_string_view<CharT,Traits>)