How to not over write an existing file with the same filename in Visual C++ with the fopen() command

If you really want to use fopen() to create a log file (which I'm sure you don't - whatever you're writing it's not C) then rather than mess about with renaming files just append the time the file was created to a base name. Then they sort nicely in a directory.

[Warning, this is going to get ugly... I'm not the best C programmer anymore, if I ever was any good]

#include <time.h>
#include <stdio.h>

#include <time.h>
#include <stdio.h>

int main()
{
	char file_name[ 128 ] = { 0, };

	int file_name_size = sprintf( file_name, "log_file_%u.txt", time( 0 ) );
	if( file_name_size < 128 && file_name_size > -1  )
	{
		FILE *fp = fopen( file_name, "w" );
		if( fp )
		{
			fputs( "Are we open?", fp );
			fclose( fp );
			fp = NULL;
		}
	}

	return 0;
}

Anyway, the point of this example is to show you that sticking with whatever your current runtime is far more productive than hacking at a lump of code to do the same thing.

Cheers,

Ash

I could suggest you name the log file with the current date/time.

The risk of collision will be very close to zero; and if you create multiple logs, it might be easier to manager.

fopen does not provide an automatic rename service, so you must program it yourself.

With function _access you can check the existence of a particular file.
With function rename you can rename an existing file.

So do something like:

if (_access ("LogFile.txt", 0) == 0)
    rename ("LogFile.txt", "LogFile.old");

Probably your code must be a little more sophisticated, otherwise you are going to run into problems when doing this multiple times. Perhaps you implement a version number scheme for the renamed files and name them LogFile.v1, LogFile.v2 etc.

Hope that gets you on the right track.