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From: alm@netcom.com (Andrew Moore)
Subject: first call to signal() returns NULL?
Message-ID: <almC5v240.92E@netcom.com>
Organization: NETCOM On-line Communication Services (408 241-9760 guest)
Date: Thu, 22 Apr 1993 01:14:20 GMT
Lines: 28
The first call to signal() returns NULL.
The following code under both 386BSD and SunOS, whether run in
foreground or background returns:
err: NULL returned first call
If run in the background, SIGINT is correctly ignored, but the first
call to signal() does not indicate this... Aside from the fact that
sigaction() should be used to probe the status of a signal, what am I
missing?
-Andrew Moore <alm@netcom.com>
#include <stdio.h>
#include <signal.h>
#ifdef __STDC__
typedef void sighandler(int);
sigfunc *signal(int, sighandler *);
#else
void (*signal())();
#endif
main() {
/* first time signal is called, it returns NULL! */
if (signal(SIGINT, SIG_IGN) != NULL)
printf("okay: non-NULL returned first call\n"), exit(1);
if (signal(SIGINT, SIG_IGN) != SIG_IGN)
printf("err: NULL returned second call\n"), exit(1);
printf("err: NULL returned first call\n");
}