Re: Safe to maintain pointer to errno() ?

On 10/14/2010 11:41 AM, Christen, Duane wrote:

I understood the discussion in this thread, http://archive.midrange.com/rpg400-l/200611/msg00396.html incorrectly. I took it as recommendation not to clear/test errNo. I think, now, though it was a best practices example. Either way though, if implemented consistently either method will work.

I agree that there is no point in setting errno in advance for functions that return an indication of failure in some other way. In those cases, it makes sense to just check errno if more information is needed about the error.

But for those functions where errno is the only way to detect failure, errno should be set to zero before calling the function.

So there are two patterns depending on the nature of the function. Use the second pattern if the API documentation doesn't provide a return value or output parameter that indicates failure.

rc = function();
if rc <> 0;
check errno
...

errno = 0;
something = function();
if errno <> 0;
...