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#include <stdio.h> /* printf and friends */
#include <fcntl.h> /* open, creat, etc */
#include <unistd.h> /* read, close */
#include <stdarg.h> /* va_* */
#include <stdlib.h> /* exit */
/* The C Programming Language: 2nd Edition
*
* Exercise 8-1: Rewrite the program `cat` from Chapter 7 using read(),
* write(), open(), and close() instead of their standard library
* equivalents. Perferm experiments to determine the relative speeds of
* the two versions.
*
* Notes: The `cat` program can be found on pp 162-163 in the book.
*/
#define DEBUG 0
char buf;
/* Let's have fewer magic numbers */
enum {
STDIN,
STDOUT,
STDERR
};
#if DEBUG == 1
/* d_printf - output a debug message
* This was shamelessly taken from the book
*/
void d_printf(char *fmt, ...) {
va_list args;
va_start(args, fmt);
fprintf(stderr, "debug: ");
vfprintf(stderr, fmt, args);
fprintf(stderr, "\n");
va_end(args);
}
#endif
void in2out() {
int status;
while ((status = read(STDIN, &buf, 1))) {
if (status != -1) {
status = write(STDOUT, &buf, 1);
if (status == -1) {
fprintf(stderr, "error: Could not write to stdout; something is very wrong.\n");
exit(1);
}
} else {
fprintf(stderr, "error: Could not read stdin; something is very wrong.\n");
}
}
}
int main(int argc, char **argv) {
int fd;
/* Remember the name we were invoked as, for messages */
ssize_t fstatus;
argv++;
#if DEBUG == 1
char *prog = *argv;
d_printf("Starting %s", prog);
#endif
if (argc == 1) {
#if DEBUG == 1
d_printf("No arguments specified; copying stdin to stdout");
#endif
in2out();
argv++;
exit(0);
}
/* The trick to understanding this is "x--" will run one more time than
* expected, because it doesn't decrement until after it's been evaluated
* for use in the expression. You can also look at it as "we've already
* pushed argv ahead by one".
*/
while (argc-- > 1) {
#if DEBUG == 1
d_printf("Trying to open %s", *argv);
#endif
fd = open(*argv, O_RDONLY, 0);
if (fd != -1) {
#if DEBUG == 1
d_printf("It was successfully opened. Reading.");
#endif
while ((fstatus = read(fd, &buf, 1))) {
if (fstatus == (-1)) {
/* Fail early, fail often */
fprintf(stderr, "error: Cannot read from '%s'. \n", *argv);
close(fd);
return 1;
}
if ((fstatus = write(STDOUT, &buf, 1)) == (-1)) {
fprintf(stderr, "error: Cannot write to stdout.\n");
close(fd);
return 1;
}
}
#if DEBUG == 1
d_printf("%s read complete.", *argv);
#endif
} else {
fprintf(stderr, "error: Could not open file '%s' for reading.\n", *argv);
close(fd);
return 1;
}
#if DEBUG == 1
d_printf("Closing file %s.", *argv);
#endif
close(fd);
argv++;
}
exit(0);
}
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