developing filter (crash on signal 11)

[michael]

Hi all
I am developing a filter, and I have some troubles.
Would someone please help?

The filter uses fwrite() to write print data to stdout, but it crashes occasionally.  The code is like this.

  fwrite( buff, 1, size, stdout );

I have checked the buff pointer, its content and the size, they are ok.
I also added ferror() and fflush() to check on stdout before calling fwrite(), but it does not work.
However it works fine, if I add many many debug messages before and after the fwrite such as

 fprintf(stderr, "DEBUG: xxxxx\n");

Can someone please give me some hint?
Is there another way to check stdout works properly before I use fwrite()?

Thanks in advance.
Michael