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# std::basic_string::npos

From cppreference.com
< cpp‎ | string‎ | 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 <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

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