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-rw-r--r--ch8/8-02_fopen-and-fillbuf.c101
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diff --git a/ch8/8-02_fopen-and-fillbuf.c b/ch8/8-02_fopen-and-fillbuf.c
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+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include "8-02_syscalls.h"
+
+/* The C Programming Language: 2nd Edition
+ *
+ * Exercise 8-2: Rewrite `fopen` and `_fillbuf` with fields instead of explicit
+ * bit operations. Compare code size and execution speed.
+ *
+ * Notes: Fields, in this case, are struct fields. I implemented them as 1-bit
+ * integers to simulate bit fields via struct.
+ *
+ * The resulting binary of this file (plus the custom header) runs through this
+ * source file in about 0.001s. However, the binary is 1KB larger.
+ */
+
+#define PERMS 0666
+
+int getc(FILE *);
+
+int my__fillbuf(my_FILE *fp) {
+ int bufsize;
+ if (fp->flags._READ == 0) {
+ return EOF;
+ }
+ bufsize = (fp->flags._UNBUF != 0) ? 1 : BUFSIZ;
+ if (fp->base == NULL) {
+ if ((fp->base = (char *) calloc(bufsize, sizeof (char))) == NULL) {
+ return EOF;
+ }
+ }
+ fp->ptr = fp->base;
+ fp->cnt = read(fp->fd, fp->ptr, bufsize);
+ if (--fp->cnt < 0) {
+ if (fp->cnt == -1) {
+ fp->flags._EOF = 1;
+ } else {
+ fp->flags._ERR = 1;
+ }
+ fp->cnt = 0;
+ return EOF;
+ }
+ return (unsigned char) *fp->ptr++;
+}
+
+my_FILE * my_fopen(char *name, char *mode) {
+ int fd;
+ my_FILE *fp;
+ if (*mode != 'r' && *mode != 'w' && *mode != 'a') {
+ return NULL;
+ }
+ for (fp = _iob; fp < _iob + FOPEN_MAX; fp++) {
+ if (fp->flags._READ == 0 && fp->flags._WRITE == 0) {
+ break;
+ }
+ }
+ if (fp >= _iob + FOPEN_MAX) {
+ return NULL;
+ }
+ if (*mode == 'w') {
+ fd = creat(name, PERMS);
+ } else if (*mode == 'a') {
+ if ((fd = open(name, O_WRONLY, 0)) == -1) {
+ fd = creat(name, PERMS);
+ }
+ lseek(fd, 0L, 2);
+ } else {
+ fd = open(name, O_RDONLY, 0);
+ }
+ if (fd == -1) {
+ return NULL;
+ }
+ fp->fd = fd;
+ fp->cnt = 0;
+ if (*mode == 'r') {
+ fp->flags._READ = 1;
+ } else {
+ fp->flags._WRITE = 1;
+ }
+ return fp;
+}
+
+int main() {
+ my_FILE *fp = my_fopen("8-02_fopen-and-fillbuf.c", "r");
+ if (fp != NULL) {
+ puts("We could read the file.\n");
+ /* pro tip: don't declare this as 'unsigned' or you'll create an
+ * endless loop thanks to EOF typically being negative. Don't waste
+ * half an hour on a newbie mistake like I did. :)
+ */
+ char c;
+ while ((c = my_getc(fp)) != EOF) {
+ putchar(c);
+ }
+ } else {
+ puts("Could not open file for reading.");
+ }
+ return 0;
+}