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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;
}
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