不抛出文件 I/O 异常

Question

i have this piece of code that trying to write into a log file.

Logger::Logger(void) //constructor
{
    try{
        log.open("lodg.txt", std::fstream::in); //Open existing file.
        this->writeLog("Logger started", Severity::INFO); //Add line to the log file,
    }catch(fstream::failure e)
    {
        cerr << "File I/O error." << endl;
        cout << e.what() << endl;
    }
}

Now i know that in this case fstream::in will not create a file if it doesn't exist, but the problem is, even though it doesn't create a new file, it doesn't throw any exception, and I'm able to "write" to file that doesn't exist, code like: log << "Write somthing"; //Not throwing any exception.

Answer 1

By default streams don't throw exceptions (in most situations this is not what you want). But you can turn them on.

// Set the states you want the stream to throw on.
log.exceptions(std::ios::fail | std::ios::bad | std::ios::eof);

Note do this before you open the file so that you throw when you attempt to open.

---

Note: Usually you want to check for failures explicityl.

log.open("File");
if (!log) {
    std::cerr << "Failed to open";
    // throw or fix error.
}