What about errno==0 ?

[Doug Gwyn]

In article <7798 at mcshh.hanse.de> bkr at mcshh.hanse.de (Bjoern Kriews) writes:
-I am want to let my code now whether a routine returning NULL on failure
-failed because of an I/O Error are for a logical mistake. For example,
-I'm setting a global variable = errno after a failed malloc(), then do
-an fclose() and return. I want to set this global to zero if the code
-failed because of any error not setting errno. 
-What does the standard say about the value 0 for errno ?
-Can I assume that there is no errno.h defining any errorcode = 0 ?

As I understand your question, the answer is that all error numbers that
may be set by standard library functions are positive integers.  Therefore
you may safely assume that a code of 0 is different from any error code.