Find Substring

std::string::find locates the first position where a smaller piece of text appears.

find_substring.cpp

#include <iostream>
#include <string>

int main() {
    std::string needle = ;

    std::string line = "app.log: ready";
    std::size_t found = line.find(needle);
    int position = found == std::string::npos ? -1 : static_cast<int>(found);

    std::cout << "needle=" << needle << std::endl;
    std::cout << "position=" << position << std::endl;
    return 0;
}

#include <iostream>
#include <string>

int main() {
    std::string needle = ;

    std::string line = "app.log: ready";
    std::size_t found = line.find(needle);
    int position = found == std::string::npos ? -1 : static_cast<int>(found);

    std::cout << "needle=" << needle << std::endl;
    std::cout << "position=" << position << std::endl;
    return 0;
}

#include <iostream>
#include <string>

int main() {
    std::string needle = ;

    std::string line = "app.log: ready";
    std::size_t found = line.find(needle);
    int position = found == std::string::npos ? -1 : static_cast<int>(found);

    std::cout << "needle=" << needle << std::endl;
    std::cout << "position=" << position << std::endl;
    return 0;
}

find `find` returns the first matching position, or `std::string::npos` when the text is not present.

position String positions are zero-based indexes.