Re: [PATCH] freopen SEGFAULT on win32 with filename == NULL

[Claudio Bley]

Bruno Haible <address@hidden> writes:

> Claudio Bley wrote:
>> --------------------
>> --- freopen.c.orig   2011-08-03 14:22:15 +0200
>> +++ freopen.c        2011-08-25 21:01:46 +0200
>> @@ -38,7 +38,7 @@
>>  rpl_freopen (const char *filename, const char *mode, FILE *stream)
>>  {
>>  #if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
>> -  if (strcmp (filename, "/dev/null") == 0)
>> +  if (filename && strcmp (filename, "/dev/null") == 0)
>>      filename = "NUL";
>>  #endif
>>  
>> --------------------
>
> Yes, thanks for the fix. I'm applying this is your name. (The "tiny change"
> mark means that the change does not warrant the exchange of a copyright
> assignment.)

Thank you.

> Claudio Bley wrote:
>> Furthermore, using NULL as filename does not work at all using the MS
>> C runtime library (debug assertion violation).
>> 
>> --------------------
>> --- freopen.c.1      2011-08-25 21:05:34 +0200
>> +++ freopen.c        2011-08-25 21:08:52 +0200
>> @@ -38,6 +38,9 @@
>>  rpl_freopen (const char *filename, const char *mode, FILE *stream)
>>  {
>>  #if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
>> +#  ifdef _MSC_VER
>> +  if (!filename) return NULL; /* would trigger a runtime error on MSVC */
>> +#  endif
>>    if (filename && strcmp (filename, "/dev/null") == 0)
>>      filename = "NUL";
>>  #endif
>> 
>> --------------------
>
> Unfortunately, freopen (NULL, ...) is not something gnulib can support
> portably.

Just to clarify. That patch only tries to avoid a runtime crash when
 trying to pass NULL as filename (when using the MSVC compiler). It
 simply makes that function fail in this case (maybe errno should be
 set too).

>> Using MinGW and trying to change stdout's mode to binary simply fails:
>> 
>> if (!isatty(fileno(stdout))
>>    freopen(NULL, "wb", stdout); /* <- returns NULL */
>
> You can use the gnulib module 'binary-io' instead of freopen here.

That's perfectly fine for me. I will talk to the diffutils people
(which is the program I'm currently having problems with). Thanks for
the pointer, I didn't realize that module already exists...

Cheers,
Claudio