#define BUFSIZZ 512

// caseC: do something that we know returns -1
// failure to make sure we understand data sizes.
// john refling.  caseC.c

/* OUTPUT: this case shows correct return value for fail

	open fake file, which fails, as expected
	fno = -1, errno = 2 'No such file or directory'

	try write() 512 to bad file, expect fail
	RV = 0xffffffffffffffff or -1, errno = 9 'Bad file descriptor'

	RV IS NOT == 0
	RV IS < 0
	RV IS == -1
	RV IS == -1L
	RV IS NOT == -1U

	can detect this failure.

*/

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <err.h>
#include <sys/fcntl.h>

int main(int argc, char *argv[]) {

	char *buf = calloc(1, BUFSIZZ);

	printf("\nopen fake file, which fails, as expected\n");
	int fno = open("/dev/flopZpy", O_RDWR, 0777);
	printf("fno = %d, errno = %d '%s'\n", fno, errno, strerror(errno));

	// write some data to bad file number

	printf("\ntry write() 512 to bad file, expect fail\n");
	errno = 0;
	ssize_t RV = write(fno, buf, BUFSIZZ);

	// print out the RV, it is a ssize_t, use %ld

	printf("RV = 0x%lx or %ld, errno = %d '%s'\n\n", (long unsigned)RV, RV, errno,
		strerror(errno));

	if (512 == RV) return(0);

	// see what constants RV matches:

	fprintf(stderr, "RV %s == 0\n", (RV == 0)?"IS":"IS NOT");
	fprintf(stderr, "RV %s < 0\n", (RV < 0)?"IS":"IS NOT");
	fprintf(stderr, "RV %s == -1\n", (RV == -1)?"IS":"IS NOT");
	fprintf(stderr, "RV %s == -1L\n", (RV == -1L)?"IS":"IS NOT");
	fprintf(stderr, "RV %s == -1U\n\n", (RV == -1U)?"IS":"IS NOT");

	fprintf(stderr, "can detect this failure.\n");

	return 0;
}