Question

I have a class FileTransfer that uses an ofstream object, log. The class’ constructor calls open() on the ofstream object, with logFileName having a default value in the .h file.

class FileTransfer {
    public:
        FileTransfer(char *logFileName = "client log.txt");
        bool sendFile();
        ofstream log;           // log file
};

FileTransfer::FileTransfer(char * logFileName) {
    this -> logFileName = logFileName;
    // Open log file
    log.open(logFileName);
}

In another class method, sendFile(), I use the stream to log events.

bool FileTransfer::sendFile() {
    log << "Sender: starting on host " << localhost << endl;
}

When I have it like this, nothing is written to the log file . I’ve tried checking log.is_open() and good() and both return true.

EDIT:

int main() {
    FileTransfer * ft = new FileTransfer(); // open() is called
    ft -> sendFile(); 
}

If I call log.open() in the method FileTransfer::sendFile() right before my output operations, then output works perfectly fine.

bool FileTransfer::sendFile() {
    log.open(logFileName);
    log << "Sender: starting on host " << localhost << endl;
}

Why does it do this?

Answer 1

Aha I know what is you problem! You are writing to the file, but actually it goes to a buffer and is not flushed in the first case (this is a bit random).

Add the following line after your printing:

log.flush();

It should fix your issue.