Thread: Instantiate FILE handler in header file

Hi,
I need to define a macro in a header file in C++ which is called lots of time in the application (for particular, thus non-negociable, log reasons).
I have created the macro as following:

Code:

#pragma once
// include statements
#define MYMACRO(one, two) {\
FILE *filepointer;\
/* code */\
filepointer = fopen("logfile.txt", "a");\
fprintf(filepointer, "%s", somemessage);\
fclose(filepointer);\
}\

The code is built and does the job it is intended for. But it opens and closes the file at each call. I want to create the 'filepointer' object, and instantiate it with the fopen() value as above, outside de macro, just before the

Code:

#define MYMACRO

statement, so that not to have to open/close each time the macro is called.
I have quickly read that this is possible by defining a class in the header, with diffferent possibilities for the instantiation. I this case I think I would also be able to take off

Code:

fclose()

(the file will be closed when application exits).
Therefore, I appreciate your contribution on how to properly implement this requirement.
Thanks!

In C++ you really should be avoiding macros in all but the rarest of circumstances and IMO the same goes for using the C-stdio functions.

While global variables are usually considered a bad practice, this might be a case where a global ofstream might be an acceptable alternative.

I this case I think I would also be able to take off fclose() (the file will be closed when application exits).

One of the benefits of using a C++ stream is that it automatically closes when the stream goes out of scope (the end of the program in this case).

Jim

Thanks Jim,
I keep my question because, as I've mentioned, I have to do so. But what would be the code then as you propose?
Thanks

Here is a very simple example (no horrible, potentially unsafe macro required).

Code:

#include <fstream>

std::ofstream log;

int main()
{
    log.open("LogFileName");

   // Write to log file.
   log << "Error: " << 23 << " Something bad happened!" << std::flush();

}

Jim

But won't that "global function" open and close the stream every time you call the function?

Jim

but so does the OP's macro.

Yes, but the purpose of this topic is to find a method to avoid the opening and closing of the stream each time the log functionality is used.

so that not to have to open/close each time the macro is called.

Jim

Is this simply for debugging purposes?