File Error Checks

A stream can be checked before reading so code can handle missing files safely.

file_error_checks.cpp

#include <cstdio>
#include <fstream>
#include <iostream>
#include <string>

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

    std::ofstream setup("present.txt");
    setup << "status=ready" << std::endl;
    setup.close();
    std::remove("missing.txt");

    std::ifstream input(filename);
    if (input) {
        std::string line;
        std::getline(input, line);
        std::cout << "opened=yes" << std::endl;
        std::cout << line << std::endl;
    } else {
        std::cout << "opened=no" << std::endl;
        std::cout << "fallback=use default" << std::endl;
    }

    std::remove("present.txt");
    return 0;
}

#include <cstdio>
#include <fstream>
#include <iostream>
#include <string>

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

    std::ofstream setup("present.txt");
    setup << "status=ready" << std::endl;
    setup.close();
    std::remove("missing.txt");

    std::ifstream input(filename);
    if (input) {
        std::string line;
        std::getline(input, line);
        std::cout << "opened=yes" << std::endl;
        std::cout << line << std::endl;
    } else {
        std::cout << "opened=no" << std::endl;
        std::cout << "fallback=use default" << std::endl;
    }

    std::remove("present.txt");
    return 0;
}

stream state check An input stream converts to `true` when the file opened successfully and to `false` when it did not.