1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
|
#include <stdio.h>
int main(int argc, unsigned char *argv[])
{
unsigned char *buf, *from, *to, *text, *subst;
FILE *fromfid, *tofid;
if (argc != 5) {
fprintf(stderr,"Usage: %s from to text replacement\n",argv[0]);
exit(1);
}
from = argv[1];
to = argv[2];
text = argv[3];
subst = argv[4];
if (strlen(text) != strlen(subst)) {
fprintf(stderr,"%s: text and substitution different lengths\n",argv[0]);
exit(1);
}
fromfid = fopen(from,"rb");
if (fromfid == NULL) {
perror(from);
exit(1);
}
tofid = fopen(to,"wb");
if (tofid == NULL) {
fclose(fromfid);
perror(to);
exit(1);
}
buf = malloc(strlen(text));
if (buf == NULL) {
fprintf(stderr,"%s: memory allocation failure", argv[0]);
fclose(fromfid);
fclose(tofid);
exit(1);
}
int pos=0;
while (1) {
int c=fgetc(fromfid);
if (c < 0) {
if (ferror(fromfid)) perror(from);
if (pos) {
if (fwrite(buf,1,pos,tofid) != pos) goto write_error;
}
fclose(fromfid);
fclose(tofid);
if (ferror(fromfid)) {
exit(1);
} else {
exit(0);
}
}
buf[pos++] = (unsigned char)c;
if (buf[pos-1] != text[pos-1]) {
/* text does not match buffer */
int i;
shift:
/* output first character of buf and shift left by 1 */
if (fputc(buf[0],tofid) < 0) goto write_error;
for (i=1; i < pos; i++) buf[i-1]=buf[i];
pos--;
/* repeat until shifted buf matches start of text */
for (i=0; i < pos; i++) if (buf[i]!=text[i]) break;
if (i<pos) goto shift;
} else if (text[pos]=='\0') {
/* text matches buffer, so write subst */
if (fwrite(subst,1,pos,tofid) != pos) goto write_error;
pos = 0;
} /* else text matches so far, check next character */
}
write_error:
perror(to);
fclose(from);
fclose(to);
exit(1);
}
|
