[Mingw-users] [mingw - C/C++] Portablity enhancement. fopen binary mode

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By: zephyrus00jp



Lately I had a non-working program when I ported a
program that runs on Solaris/Linux and a few other platforms
including CYGWIN to non-CYGWIN mingw platorm using the
-mno-cygwin switch to mingw GCC compiler.

After a long debugging sessions, it turns out that
I have not specified "b" in the second argument
to fopen 

Wrong! 
	fopen(filename, "r")
	fopen(filename, "w")
	fopen(filename, "w+r")

Correct!
	fopen(filename, "rb")
	fopen(filename, "wb")
	fopen(filename, "w+rb")


I initially suspected buggy mingw runtime since
the same program works like a charm under cygwin environment.

I now recall CYGWIN decided to do away with the distinction
of text-mode and binary mode and now supports only
binary mode (that is, the cygwin runtime assumes that you 
intend to have binary mode fopen even if you say, "r", "w", etc. without having
"b" in the string. The cygwin runtime
takes care of the missing "b" and adds it internally, so
to speak.).
I think it is a clever move to avoid porting problems like
the one I experience here.

Will mingw developers consider such modification of
the interface provided by mingw runtime?

Or if doing away the text and binry modes distinction
is too much (since some windows programmers may
depend on it),
will developers be interested in providing
some kind of wrappers like the following?

This will warn the programmers about
the missing "b" when people port programs from
other platforms.
They can disable such warning by setting
the value of a global variable. So it is a good reminder, but
can be made silent.

The following is a rough outline of the
code , but you will get the idea.

In the header somewhere:

extern void * __mingw32_check_fopen_mode(char *m);
#define fopen(f,m)  fopen(f,__mingw32_check_fopen_mode(m))

In the runtime library.

int __mingw32_c_f_m_shutup;

void * 
__mingw32_check_fopen_mode(char *m)
{
	
  if(__mingw32_c_f_m_shutup == 0 &&  strchr(m, "b") == NULL)
	{
	/* We may want to use write() directly instead of using
	   stderr, but you get the idea here.*/

	fprintf(stderr,"The second argument to fopen, '%s' doesn't contain \b\. \n",
m);
        fprintf(stderr,"We suggest you add it for maximum compatibility with
other platforms. \n");
	fprintf(stderr,"You can silence this message by setting a global variable int
__mingw32_c_f_m_shutup to 1.\n");

	}

	return m;
}


You can simply concatenate "b" to the argument m
by copying m into a static array of a suitable size and
then add "b" at the end to provide CYGWIN-like
"forget text-mode vs binary mode distinction" support.
Mabye if we set 
__mingw32_c_f_m_shutup
to 2, we could do that automatically and return
the concatenated string as the value passed to
fopen.

Any way, thank you for the great package and
I hope my suggestion here might
be helpful to future programmers who
port programs from other platforms to mingw environment.


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