An attempt to use the sigpending function

Question

I wrote a program that uses the sigpending () function. The program returns blocked or pending signals.

My question is, what else could I improve or what problems does implementation have? Possible bugs?

code:

#include <signal.h>
#include <stdio.h>
#include <unistd.h>
void catcher(int signum) {
 puts("inside catcher!");
 if (signum != 0)
 perror("signum error");
}
void check_pending(int signum, char * signame) {
 sigset_t sigset;
 if (sigpending( & sigset) != 0)
 perror("sigpending() error");
 else if (sigismember( & sigset, signum))
 printf("a %s signal is pending\n", signame);
 else
 printf("no %s signals are pending\n", signame);
}
int main() {
 struct sigaction sigact;
 sigset_t sigset;
 sigemptyset( & sigact.sa_mask);
 sigact.sa_flags = 0;
 sigact.sa_handler = catcher;
 if (sigaction(SIGUSR1, & sigact, NULL) != 0)
 perror("sigaction() error");
 else {
 sigemptyset( & sigset);
 sigaddset( & sigset, SIGUSR1);
 if (sigprocmask(SIG_SETMASK, & sigset, NULL) != 0)
 perror("sigprocmask() error");
 else {
 puts("SIGUSR1 signals are now blocked");
 kill(getpid(), SIGUSR1);
 printf("after kill: ");
 check_pending(SIGUSR1, "SIGUSR1");
 sigemptyset( & sigset);
 sigprocmask(SIG_SETMASK, & sigset, NULL);
 puts("SIGUSR1 signals are no longer blocked");
 check_pending(SIGUSR1, "SIGUSR1");
 }
 }
}

Answer 1

what else could I improve or what problems does implementation have?

Just some little ideas. Sorry, not much sig...() feedback.

---

Lack of documentation

At least some comments in the .c file to indicate overall functionality.

Use const

Use const to allow call with a const char * and to better convey function's use of signame.

// void check_pending(int signum, char * signame)
void check_pending(int signum, const char * signame)

Clearer message

Consider a sentence and not lower case.

Example below, but applies to other output as well.

// printf("a %s signal is pending\n", signame);
printf("A %s signal is pending.\n", signame);

From time-to-time and especially in error messages, it is really nice to see a string printed with sentinels (like quote-marks). It is useful in seeing what part of output is format and what is data.

printf("A \"%s\" signal is pending.\n", signame);

In error message this in even more important as something went wrong. Maybe the string has unexpected leading/trailing white-space that is messing up the operation?

Fully initialize

Consider these 2 code snippets. The 2nd one fully initializes sigact- even members that are not obviously important.

// OP
struct sigaction sigact;
sigemptyset( & sigact.sa_mask);
sigact.sa_flags = 0;
sigact.sa_handler = catcher;
// Suggested
// This initializes all members, not just .sa_flags, .sa_handler.
struct sigaction sigact = { .sa_flags = 0, .sa_handler = catcher };
sigemptyset( & sigact.sa_mask);

Define in needed block, not above

// sigset_t sigset;
...
else {
 sigset_t sigset;
 sigemptyset( & sigset);

Error check

kill(), sigprocmask(), and other process functions deserve a check of their return values.

Error return

After perror("sigprocmask() error");, I'd expect a different return value like return EXIT_FAILURE; so calling scripts can differentiate.

Style

There are various style issues that I do not prefer like: missing {} on one-liners, void-less main(), spaced use of unary &, pointer *, 4-space indent. Yet it is more important to employ a constant style than to promote my preference. OP's code is consistent and that is good.

I do like subtle good style bits like alphabetized include.