From 4ad4e6c7f6d2fb414d22dd3e55801c85b02c1af7 Mon Sep 17 00:00:00 2001
From: zlg <zlg@zlg.space>
Date: Sat, 22 Dec 2018 01:23:35 -0800
Subject: Solve Exercise 8-2: fopen and fillbuf
---
ch8/8-02_fopen-and-fillbuf.c | 101 ++++++++++++++++++++++++++++++++++++
ch8/8-02_stdlib-fopen-and-fillbuf.c | 33 ++++++++++++
ch8/8-02_syscalls.h | 47 +++++++++++++++++
3 files changed, 181 insertions(+)
create mode 100644 ch8/8-02_fopen-and-fillbuf.c
create mode 100644 ch8/8-02_stdlib-fopen-and-fillbuf.c
create mode 100644 ch8/8-02_syscalls.h
diff --git a/ch8/8-02_fopen-and-fillbuf.c b/ch8/8-02_fopen-and-fillbuf.c
new file mode 100644
index 0000000..e533da8
--- /dev/null
+++ b/ch8/8-02_fopen-and-fillbuf.c
@@ -0,0 +1,101 @@
+#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;
+}
diff --git a/ch8/8-02_stdlib-fopen-and-fillbuf.c b/ch8/8-02_stdlib-fopen-and-fillbuf.c
new file mode 100644
index 0000000..2219757
--- /dev/null
+++ b/ch8/8-02_stdlib-fopen-and-fillbuf.c
@@ -0,0 +1,33 @@
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.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: This file uses the standard library exclusively, in contrast to the
+ * partial replacement solution in the other 8-02 files.
+ *
+ * The resulting binary of this file executes in about 0.001s, just like the
+ * partial replacement solution. Its binary is 1KB smaller, however.
+ */
+int main() {
+ FILE *fp = 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 = getc(fp)) != EOF) {
+ putchar(c);
+ }
+ } else {
+ puts("Could not open file for reading.");
+ }
+ return 0;
+}
diff --git a/ch8/8-02_syscalls.h b/ch8/8-02_syscalls.h
new file mode 100644
index 0000000..728c5af
--- /dev/null
+++ b/ch8/8-02_syscalls.h
@@ -0,0 +1,47 @@
+/* 8-02_syscalls.h
+ *
+ * A simpler stdio.h to aid in exercises 8-2
+ */
+
+long lseek(int fd, long offset, int origin);
+
+struct _flags {
+ unsigned int _READ : 1;
+ unsigned int _WRITE : 1;
+ unsigned int _UNBUF : 1;
+ unsigned int _EOF : 1;
+ unsigned int _ERR : 1;
+} flags;
+
+typedef struct _iobuf {
+ int cnt;
+ char *ptr;
+ char *base;
+ struct _flags flags;
+ int fd;
+} my_FILE;
+
+my_FILE _iob[FOPEN_MAX] = {
+ /* stdin is read-only */
+ { 0, (char *) 0, (char *) 0, {1, 0, 0, 0, 0}, 0 },
+ /* stdout is write only */
+ { 0, (char *) 0, (char *) 0, {0, 1, 0, 0, 0}, 1 },
+ /* stderr is written AND not buffered */
+ { 0, (char *) 0, (char *) 0, {0, 1, 1, 0, 0}, 2 }
+};
+
+#define feof(p) (((p)->flags._EOF) != 0)
+#define ferror(p) (((p)->flags._ERR) != 0)
+#define fileno(p) ((p)->fd)
+#define my_getc(p) (--(p)->cnt >= 0 ? (unsigned char) *(p)->ptr++ : my__fillbuf(p))
+#define getchar() getc(stdin)
+
+int my_fempty(struct _flags flags) {
+ if (!flags._READ && !flags._WRITE && !flags._UNBUF && !flags._EOF && !flags._ERR) {
+ return 1;
+ } else {
+ return 0;
+ }
+}
+
+int my_fclose(my_FILE*);
--
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