new files

Task/Detect-division-by-zero/C/detect-division-by-zero.c

@@ -0,0 +1,100 @@
+#include <limits.h>	/* INT_MIN */
+#include <setjmp.h>	/* siglongjmp(), sigsetjmp() */
+#include <stdio.h>	/* perror(), printf() */
+#include <stdlib.h>	/* exit() */
+#include <signal.h>	/* sigaction(), sigemptyset() */
+
+static sigjmp_buf fpe_env;
+
+/*
+ * This SIGFPE handler jumps to fpe_env.
+ *
+ * A SIGFPE handler must not return, because the program might retry
+ * the division, which might cause an infinite loop. The only safe
+ * options are to _exit() the program or to siglongjmp() out.
+ */
+static void
+fpe_handler(int signal, siginfo_t *w, void *a)
+{
+	siglongjmp(fpe_env, w->si_code);
+	/* NOTREACHED */
+}
+
+/*
+ * Try to do x / y, but catch attempts to divide by zero.
+ */
+void
+try_division(int x, int y)
+{
+	struct sigaction act, old;
+	int code;
+	/*
+	 * The result must be volatile, else C compiler might delay
+	 * division until after sigaction() restores old handler.
+	 */
+	volatile int result;
+
+	/*
+	 * Save fpe_env so that fpe_handler() can jump back here.
+	 * sigsetjmp() returns zero.
+	 */
+	code = sigsetjmp(fpe_env, 1);
+	if (code == 0) {
+		/* Install fpe_handler() to trap SIGFPE. */
+		act.sa_sigaction = fpe_handler;
+		sigemptyset(&act.sa_mask);
+		act.sa_flags = SA_SIGINFO;
+		if (sigaction(SIGFPE, &act, &old) < 0) {
+			perror("sigaction");
+			exit(1);
+		}
+
+		/* Do division. */
+		result = x / y;
+
+		/*
+		 * Restore old hander, so that SIGFPE cannot jump out
+		 * of a call to printf(), which might cause trouble.
+		 */
+		if (sigaction(SIGFPE, &old, NULL) < 0) {
+			perror("sigaction");
+			exit(1);
+		}
+
+		printf("%d / %d is %d\n", x, y, result);
+	} else {
+		/*
+		 * We caught SIGFPE. Our fpe_handler() jumped to our
+		 * sigsetjmp() and passes a nonzero code.
+		 *
+		 * But first, restore old handler.
+		 */
+		if (sigaction(SIGFPE, &old, NULL) < 0) {
+			perror("sigaction");
+			exit(1);
+		}
+
+		/* FPE_FLTDIV should never happen with integers. */
+		switch (code) {
+		case FPE_INTDIV: /* integer division by zero */
+		case FPE_FLTDIV: /* float division by zero */
+			printf("%d / %d: caught division by zero!\n", x, y);
+			break;
+		default:
+			printf("%d / %d: caught mysterious error!\n", x, y);
+			break;
+		}
+	}
+}
+
+/* Try some division. */
+int
+main()
+{
+	try_division(-44, 0);
+	try_division(-44, 5);
+	try_division(0, 5);
+	try_division(0, 0);
+	try_division(INT_MIN, -1);
+	return 0;
+}