我尝试编写一个可以替换字符串中某些单词或字符的代码。虽然输出似乎很好，但使用valgrind时出现了一些错误。有人可以帮忙吗？
01: #include <stdio.h>
02: #include <stdlib.h>
03: #include <string.h>
04:
05: char *changewords (char *sentence, char *find, char *replace)
06: {
07: size_t len_total = 0;
08:
09: char *dest = malloc (len_total + 1);
10: char *destptr = dest;
11:
12: *dest = 0;
13:
14: while (*sentence)
15: {
16: if (!strncmp (sentence, find, strlen(find)))
17: {
18: len_total += strlen(replace);
19: dest = realloc(dest, len_total + 1);
20: *destptr = 0;
21: strcat (destptr, replace);
22: sentence += strlen(find);
23: destptr += strlen(replace);
24: } else
25: {
26: len_total++;
27: dest = realloc(dest, len_total + 1);
28: *destptr = *sentence;
29: destptr++;
30: sentence++;
31: }
32:
33: }
34: *destptr = 0;
35: return dest;
36: }
37:
38: int main (void)
39: {
40: char *result;
41:
42: result = changewords ("i like it", "i", "ooooooooo");
43: printf ("%s\n", result);
44: free (result);
45: }
==20396== Invalid write of size 1
==20396== at 0x40076F: changewords (changeword4.c:22)
==20396== by 0x400815: main (changeword4.c:45)
==20396== Address 0x5204040 is 0 bytes inside a block of size 1 free'd
==20396== at 0x4C2FD5F: realloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==20396== by 0x400766: changewords (changeword4.c:21)
==20396== by 0x400815: main (changeword4.c:45)
==20396== Block was alloc'd at
==20396== at 0x4C2DB8F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==20396== by 0x400701: changewords (changeword4.c:11)
==20396== by 0x400815: main (changeword4.c:45)
==20396==
==20396== Invalid read of size 1
==20396== at 0x4C30C04: strcat (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==20396== by 0x400784: changewords (changeword4.c:23)
==20396== by 0x400815: main (changeword4.c:45)
==20396== Address 0x5204040 is 0 bytes inside a block of size 1 free'd
==20396== at 0x4C2FD5F: realloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==20396== by 0x400766: changewords (changeword4.c:21)
==20396== by 0x400815: main (changeword4.c:45)
==20396== Block was alloc'd at
==20396== at 0x4C2DB8F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==20396== by 0x400701: changewords (changeword4.c:11)
==20396== by 0x400815: main (changeword4.c:45)
==20396==
==20396== Invalid write of size 1
==20396== at 0x4C30C30: strcat (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==20396== by 0x400784: changewords (changeword4.c:23)
==20396== by 0x400815: main (changeword4.c:45)
==20396== Address 0x5204040 is 0 bytes inside a block of size 1 free'd
==20396== at 0x4C2FD5F: realloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==20396== by 0x400766: changewords (changeword4.c:21)
==20396== by 0x400815: main (changeword4.c:45)
==20396== Block was alloc'd at
==20396== at 0x4C2DB8F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==20396== by 0x400701: changewords (changeword4.c:11)
==20396== by 0x400815: main (changeword4.c:45)
==20396==
==20396== Invalid write of size 1
==20396== at 0x4C30C3F: strcat (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==20396== by 0x400784: changewords (changeword4.c:23)
==20396== by 0x400815: main (changeword4.c:45)
==20396== Address 0x5204049 is 8 bytes after a block of size 1 free'd
==20396== at 0x4C2FD5F: realloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==20396== by 0x400766: changewords (changeword4.c:21)
==20396== by 0x400815: main (changeword4.c:45)
==20396== Block was alloc'd at
==20396== at 0x4C2DB8F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==20396== by 0x400701: changewords (changeword4.c:11)
==20396== by 0x400815: main (changeword4.c:45)
==20396==
==20396== Invalid write of size 1
==20396== at 0x4007D2: changewords (changeword4.c:30)
==20396== by 0x400815: main (changeword4.c:45)
==20396== Address 0x5204049 is 8 bytes after a block of size 1 free'd
==20396== at 0x4C2FD5F: realloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==20396== by 0x400766: changewords (changeword4.c:21)
==20396== by 0x400815: main (changeword4.c:45)
==20396== Block was alloc'd at
==20396== at 0x4C2DB8F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==20396== by 0x400701: changewords (changeword4.c:11)
==20396== by 0x400815: main (changeword4.c:45)
==20396==
==20396== Invalid write of size 1
==20396== at 0x4007F1: changewords (changeword4.c:36)
==20396== by 0x400815: main (changeword4.c:45)
==20396== Address 0x5204061 is 17 bytes after a block of size 16 in arena "client"
==20396==
==20396==
==20396== HEAP SUMMARY:
==20396== in use at exit: 0 bytes in 0 blocks
==20396== total heap usage: 11 allocs, 11 frees, 1,215 bytes allocated
==20396==
==20396== All heap blocks were freed -- no leaks are possible
==20396==
==20396== For counts of detected and suppressed errors, rerun with: -v
==20396== ERROR SUMMARY: 43 errors from 6 contexts (suppressed: 0 from 0)
ooooooooo loooooooooke ooooooooot
答案 0 :(得分：2)
char *dest = malloc (len_total + 1);
char *destptr = dest;
好的，destptr指向dest指向的块。
dest = realloc(dest, len_total + 1);
*destptr = *sentence;
当您指向刚刚重新分配的块时，您取消引用destptr。这不可能是正确的。首先交换最后两个语句的顺序。