Question

I have a small code with some file I/O

bool loadConfigFile(std::string configFileName)
{
    std::ifstream configFile;
    try
    {
        configFile.open(configFileName, std::ifstream::in);
        if(true != configFile.good())
        {
            throw std::exception("Problem with config file");
        }
    } catch (std::exception &e)
    {
        fprintf(stderr, "There was an error while opening the file: %s\n %s\n" , configFileName, e.what());
        configFile.close();
    }

    configFile.close();
    return true;
}

And everytime I launch the program without the file provided as a parameter I get some rubbish on output (random characters) or an unexpected error in runtime. What am I doing wrong here ?

Answer 1

"%s" expects an null terminated char array as its input but the code is passing configFileName, which is a std::string. Either use std::string::.c_str() or use std::cerr instead:

std::cerr << "There was an error while opening the file: "
          << configFileName << '\n'
          << e.what()       << '\n';

Note that the ifstream constructor has a variant that accepts the filename to open and the destructor will close the stream if it is open so the explicit calls to open() and close() can be omitted:

try
{
    std::ifstream configFile(configFileName);
    if (!configFile.is_open())
    {
        throw std::exception("Failed to open '" + configFileName + "'");
    }
}
catch (const std::exception& e)
{
    // Handle exception.
    std::cerr << e.what() << '\n';
    return false;
}