Check file handle in C using system calls

chp2/select.c

@@ -0,0 +1,65 @@
+#include <stdio.h>
+#include <sys/time.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#define TIMEOUT 5
+#define BUF_LEN 1024
+
+int main(void) {
+	struct timeval tv;
+	fd_set readfds;
+	int ret;
+
+	/* Wait on stdin for intput. */
+	FD_ZERO(&readfds);
+	FD_SET(STDIN_FILENO, &readfds);
+	
+	/* Wait up to file seconds */
+	tv.tv_sec = TIMEOUT;
+	tv.tv_usec = 0;
+
+	/* All right, now block! */
+	ret = select(
+		STDIN_FILENO + 1,
+		&readfds,
+		NULL,
+		NULL,
+		&tv
+	);
+	if (ret == -1) {
+		perror("select");
+		return 1;
+	} else if (!ret) {
+		printf("%d seconds elapsed.\n", TIMEOUT);
+		return 0;
+	}
+
+	/*
+	 * Is our file descriptor ready to read?
+	 * (It must be, as it was the only fd that
+	 * we provided and the call returned
+	 * nonzero, but we will humor ourselves.)
+	 */
+	if (FD_ISSET(STDIN_FILENO, &readfds)) {
+		char buf[BUF_LEN+1];
+		int len;
+
+		/* guaranteed to not block */
+		len = read(STDIN_FILENO, buf, BUF_LEN);
+		if (len == -1) {
+			perror("read");
+			return 1;
+		}
+
+		if (len) {
+			buf[len] = '\0';
+			printf("read: %s\n", buf);
+		}
+		
+		return 0;
+	}
+
+	fprintf(stderr, "This should not happen!\n");
+	return 1;
+}