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If the request to register a signal handler can be honored, the signal() function returns the value of the signal handler for the most recent successful call to the signal() function for the specified signal. Otherwise, a value of
SIG_ERR is returned and a positive value is stored in errno.
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#include <signal.h>
#include <stdlib.h>
#include <string.h>
typedef void (*pfv)(int);
void handler(int signum) {
pfv old_handler = signal(signum, handler);
if (old_handler == SIG_ERR) {
perror("SIGINT handler"); /* undefined behavior */
/* handle error condition */
}
strcpy(err_msg, "SIGINT encountered.");
}
int main(void) {
pfv old_handler = signal(SIGINT, handler);
if (old_handler == SIG_ERR) {
perror("SIGINT handler");
/* handle error condition */
}
/* main code loop */
return 0;
}
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The call to perror() from handler() also violates SIG30-C. Call only asynchronous-safe functions within signal handlers.
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