[Info-vax] C compiler question

[John E. Malmberg]

On 7/27/2019 11:57 AM, Mark Berryman wrote:
> Something I see all the time when porting unix code is something similar 
> to the following:
> 
> unsigned int x;
> .
> .
> .
> if (x <= 0) {something}
> 
> This, of course, generates a QUESTCOMPARE informational.  I'm wondering 
> what code the compiler generates in such a case.  Does it treat the 
> variable as if it had been declared signed or does it do something else? 
>   Is the compiler's behavior in this case defined by a standard or is it 
> left up to the implementation?

By the standard.  "x" gets promoted to a signed type which preserves the 
negative value.

This is unavoidable in porting code since many standard routines are 
allowed to have a prototype return an unsigned type, yet specify a 
negative value for errors.

> Part of what I am wondering is if I can count on the code generated by a 
> VMS compiler to function the same as the code generated by a gcc or 
> clang compiler.

I had the same concerns until the relevant section of the C standard was 
shown to me.  I think it was on comp.os.vms that I may have asked about 
it a few years ago.

Regards,
-John
wb8tyw at qsl.net_work