1 /* $xMach: strnsubst.c,v 1.3 2002/02/23 02:10:24 jmallett Exp $ */
2
3 /*
4 * Copyright (c) 2002 J. Mallett. All rights reserved.
5 * You may do whatever you want with this file as long as
6 * the above copyright and this notice remain intact, along
7 * with the following statement:
8 * For the man who taught me vi, and who got too old, too young.
9 */
10
11 #include <sys/cdefs.h>
12 #include <err.h>
13 #include <stdbool.h>
14 #include <stdlib.h>
15 #include <string.h>
16 #include <unistd.h>
17
18 bool strnsubst(char **, const char *, const char *, size_t);
19
20 /*
21 * Replaces str with a string consisting of str with match replaced with
22 * replstr as many times as can be done before the constructed string is
23 * maxsize bytes large. It does not free the string pointed to by str, it
24 * is up to the calling program to be sure that the original contents of
25 * str as well as the new contents are handled in an appropriate manner.
26 * If replstr is NULL, then that internally is changed to a nil-string, so
27 * that we can still pretend to do somewhat meaningful substitution.
28 *
29 * Returns true if truncation was needed to do the replacement, false if
30 * truncation was not required.
31 */
32 bool
strnsubst(char ** str,const char * match,const char * replstr,size_t maxsize)33 strnsubst(char **str, const char *match, const char *replstr, size_t maxsize)
34 {
35 char *s1, *s2, *this;
36 bool error = false;
37
38 s1 = *str;
39 if (s1 == NULL)
40 return false;
41 /*
42 * If maxsize is 0 then set it to the length of s1, because we have
43 * to duplicate s1. XXX we maybe should double-check whether the match
44 * appears in s1. If it doesn't, then we also have to set the length
45 * to the length of s1, to avoid modifying the argument. It may make
46 * sense to check if maxsize is <= strlen(s1), because in that case we
47 * want to return the unmodified string, too.
48 */
49 if (maxsize == 0) {
50 match = NULL;
51 maxsize = strlen(s1) + 1;
52 }
53 s2 = calloc(1, maxsize);
54 if (s2 == NULL)
55 err(1, "calloc");
56
57 if (replstr == NULL)
58 replstr = "";
59
60 if (match == NULL || replstr == NULL || maxsize == strlen(s1)) {
61 strlcpy(s2, s1, maxsize);
62 goto done;
63 }
64
65 for (;;) {
66 this = strstr(s1, match);
67 if (this == NULL)
68 break;
69 if ((strlen(s2) + strlen(s1) + strlen(replstr) -
70 strlen(match) + 1) > maxsize) {
71 strlcat(s2, s1, maxsize);
72 error = true;
73 goto done;
74 }
75 strncat(s2, s1, (uintptr_t)this - (uintptr_t)s1);
76 strcat(s2, replstr);
77 s1 = this + strlen(match);
78 }
79 strcat(s2, s1);
80 done:
81 *str = s2;
82 return error;
83 }
84
85 #ifdef TEST
86 #include <stdio.h>
87
88 int
main(void)89 main(void)
90 {
91 char *x, *y, *z, *za;
92
93 x = "{}%$";
94 strnsubst(&x, "%$", "{} enpury!", 255);
95 y = x;
96 strnsubst(&y, "}{}", "ybir", 255);
97 z = y;
98 strnsubst(&z, "{", "v ", 255);
99 za = z;
100 strnsubst(&z, NULL, za, 255);
101 if (strcmp(z, "v ybir enpury!") == 0)
102 printf("strnsubst() seems to work!\n");
103 else
104 printf("strnsubst() is broken.\n");
105 printf("%s\n", z);
106 free(x);
107 free(y);
108 free(z);
109 free(za);
110 return 0;
111 }
112 #endif
113