‘npos’ is not a member of ‘std’

#include <iostream>
#include <string>

int main() {
    std::string str = "Hello, World!";

    size_t found = str.find("abc");
    if (found != std::string::npos) {
        std::cout << "Substring found at position " << found << std::endl;
    } else {
        std::cout << "Substring not found" << std::endl;
    }

    return 0;
}