Question

I am developing a GUI app on WinXP but unfortunately std::cerr/cout goes nowhere. I would like to add a simple debug method that appends messages to a log file.

I have been hashing together an almost workable solution reading other posts. And am able to have a single debug() method call in my GUI app. However, don’t even get that far in the below example app I am trying to use to find a solution.

Using:

• Dev-C++ v4.9.9.2
• WinXP

Below is the structure of my example app:

C:.
|   Makefile.win
|   Project1.dev
|
\---src
    |   bar.cpp
    |   bar.h
    |   foo.cpp
    |   foo.h
    |   main.cpp
    |
    +---inc
    |       debug.h
    |
    \---log

src/bar.h:

#ifndef BAR_H
#define BAR_H

class Bar
{
public:
    Bar();  
};
#endif

src/bar.cpp:

#include "bar.h"

Bar::Bar()
{
//    debug("I am Bar.");
}

src/foo.h and src/foo.cpp are the same except change ‘Bar’ to ‘Foo’

Using information that I have found in other articles…

src/inc/debug.h:

#ifndef MY_DEBUG_H
#define MY_DEBUG_H

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

#ifndef LOGFILE
#define LOGFILE std::ofstream logfile("log/debug.txt", std::ios::app);
#endif

#ifndef debug
#define debug(s) LOGFILE << "[" << __DATE__ << " " << __TIME__ \
            << "] " << __FILE__ << ":" << __LINE__ << " " << s << std::endl

#endif

#endif

src/main.cpp:

#include "inc/debug.h"
#include "foo.h"
#include "bar.h"

#include <iostream>

int main (int argc, char **argv)
{
    debug("Starting program."); 
    Foo *f = new Foo();
    Bar *b = new Bar();
}

When I attempt to compile this I get an error at the debug("Starting program."); line in main.cpp saying expected primary-expression before '<<' token.

Could someone tell me what causes this error and also a good way to then be able to apply debug messages in other files/classes i.e. uncomment the lines:

//    debug("I am Bar.");
//    debug("I am Foo.");

in bar.cpp and foo.cpp respectively and use debug() anywhere else?

Thanks for any help.

Answer 1

Your define for logfile is messed up.

When your code is preprocessed you’ll get:

std::ofstream logfile("log/debug.txt", std::ios::app); << "[" << __DATE__ << " " << __TIME__ \
        << "] " << __FILE__ << ":" << __LINE__ << " " << "Starting Program" << std::endl;

What you would need to do is something like this in a header file:

extern std::ofstream LOG_FILE;

and in some cpp file (perhaps your main.cpp file):

#include "debug.h"
std::ofstream LOG_FILE("log/debug.txt",std::ios::app);

To disable debugging you could do something like:

#define debug(ignore)((void) 0)

When your debug flag isn’t enabled compared to your other debug definition.

You could also put the class initialization in a similar #ifdef block to avoid opening the file when you aren’t using it.