Issue 0055: Must the SIG* macros have distinct values?

This issue has been automatically converted from the original issue lists and some formatting may not have been preserved.

Authors: Loren Schall, Project Editor (P.J. Plauger)
Date: 1993-04-14
Submitted against: C90
Status: Fixed
Fixed in: C90 TC1
Converted from: dr.htm, dr_055.html

It has been suggested that the six macros SIGABRT, SIGFPE, SIGILL, SIGINT, SIGSEGV, and SIGTERM must have distinct values. Here is the relevant portion of subclause 7.7:

“The macros defined are

SIG_DFL
                SIG_ERR
                SIG_IGN

which expand to constant expressions with distinct values that have type compatible with the second argument to and the return value of the signal function, and whose value compares unequal to the address of any declarable function; and the following, each of which expands to a positive integral constant expression that is the signal number corresponding to the specified condition:

...

An implementation need not generate any of these signals, except as a result of explicit calls to the raise function.”

On the one hand, the reference to “the signal number corresponding to the specified condition” might be assumed to imply different numbers for each signal. On the other hand, the words “distinct values” were explicitly used for the three SIG_* macros and are conspicuously missing for the others.

Also, I think it's worth noting that the standard expects raise to work meaningfully (i.e. to be able to tell them apart).

Summary: must SIGABRT, SIGFPE, SIGILL, SIGINT, SIGSEGV, and SIGTERM have distinct values?

Comment from WG14 on 1997-09-23:

Correction

In subclause 7.7, page 120, lines 14-16, change:

and the following, each of which expands to a positive integral constant expression that is the signal number corresponding to the specified condition:

to:

and the following, which expand to positive integral constant expressions with distinct values that are the signal numbers, each corresponding to the specified condition: