Question

I am trying to modify my log class to accept variables in my string. For example, if I wanted to output that there are 7 players in an area.

Here is my write to log function:

void Log::writeSuccess(string text,...)
{
    // Write the sucessfull operation to the logfile
    logfile << "<---> " << text << endl;
}

And here is my calling code:

int playernum = 7;

errorLog.writeSuccess("There are %i players in the area", playernum);

It just ends up outputting to the file: There are %i players in the area

Any way to fix this?

Answer 1

In case you can’t or won’t use boost:

void Log::writeSuccess(const char* const fmt, ...) {
    va_list ap;
    va_start(ap, fmt);
    char buff[1024];
    vsnprintf(buff, sizeof(buff), fmt, ap);
    logfile << buff;
}

Note: it assumes that the written length is limited.

Update: with gcc it’s possible to do this in a type-safe way, you need the following declaration.

class Log {
    void writeSuccess(const char* const fmt, ...) __attribute__ ((format (printf, 2, 3)));
    //...
};

Info here. Note: it’s a warning, not a compile error. If you ignore warnings that’s your problem..:)