我开发了一个动态字符串，可以用c编程语言调整大小，但我有一些无效的读取，valgrind向我报告，我试图找出原因，但我失败了：
PS：程序正在运行。
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "error.h"
#include "dstring.h"
#define DEFAULT_SIZE 512
struct dstring {
char *str;
char *estr;
size_t msize;
};
lgw_return lgw_init_dstring(struct dstring **dstr, const char *data)
{
size_t len;
if((*dstr = malloc(sizeof *dstr)) == NULL)
return LGW_ERROR_MALLOC;
if(data != NULL) {
// intiliaze dstring with value of data
len = strlen(data);
if(((*dstr)->str = malloc(len + DEFAULT_SIZE)) == NULL) {
free(*dstr);
return LGW_ERROR_MALLOC;
}
strcpy((*dstr)->str, data);
(*dstr)->estr = (*dstr)->str + len;
(*dstr)->msize = len + DEFAULT_SIZE;
}
else {
// create empty dstring
if(((*dstr)->str = malloc(DEFAULT_SIZE)) == NULL) {
free(*dstr);
return LGW_ERROR_MALLOC;
}
*((*dstr)->str) = '\0';
(*dstr)->estr = (*dstr)->str;
(*dstr)->msize = DEFAULT_SIZE;
}
return LGW_SUCCESS;
}
lgw_return lgw_destroy_dstring(struct dstring **dstr)
{
free((*dstr)->str);
free(*dstr);
*dstr = NULL;
return LGW_SUCCESS;
}
lgw_return lgw_write_dstring(struct dstring *dstr, const char *data, size_t off)
{
size_t datalen = strlen(data);
char *tmp_str;
//if offset is beyond the '\0' char return error
if(off > dstr->estr - dstr->str)
return LGW_OUT_OF_RANGE;
if(off + datalen > dstr->msize) {
if((tmp_str = realloc(dstr->str, dstr->msize +
datalen + DEFAULT_SIZE)) == NULL)
return LGW_ERROR_MALLOC;
dstr->str = tmp_str;
dstr->msize += datalen + DEFAULT_SIZE;
}
strcpy(dstr->str + off, data);
dstr->estr = dstr->str + off + datalen;
return LGW_SUCCESS;
}
lgw_return lgw_append_dstring(struct dstring *dstr, const char *data)
{
return lgw_write_dstring(dstr, data, dstr->estr - dstr->str);
}
const char *lgw_get_dstring(struct dstring *dstr)
{
return (const char *)(dstr->str);
}
#ifndef DSTRING_H_INCLUDED
#define DSTRING_H_INCLUDED
#include "error.h"
typedef struct dstring DynamicString;
lgw_return lgw_init_dstring(struct dstring **dstr, const char *data);
lgw_return lgw_destroy_dstring(struct dstring **dstr);
lgw_return lgw_write_dstring(struct dstring *dstr, const char *data, size_t off);
lgw_return lgw_append_dstring(struct dstring *dstr, const char *data);
const char *lgw_get_dstring(struct dstring *dstr);
#endif
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "error.h"
#include "dstring.h"
int main()
{
lgw_return rc;
DynamicString *s;
if((rc =lgw_init_dstring(&s, "test")) != LGW_SUCCESS) {
fprintf(stderr, "ERROR : %s", lgw_strerror(rc));
exit(EXIT_FAILURE);
}
lgw_append_dstring(s, "123");
const char *str = lgw_get_dstring(s);
printf("value is : %s\n", str);
lgw_destroy_dstring(&s);
}
==6919== Memcheck, a memory error detector
==6919== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==6919== Using Valgrind-3.10.0 and LibVEX; rerun with -h for copyright info
==6919== Command: ./a.out
==6919==
==6919== Invalid write of size 8
==6919== at 0x40084A: lgw_init_dstring (dstring.c:33)
==6919== by 0x400AD7: main (test.c:14)
==6919== Address 0x51de048 is 0 bytes after a block of size 8 alloc'd
==6919== at 0x4C28C20: malloc (vg_replace_malloc.c:296)
==6919== by 0x4007A0: lgw_init_dstring (dstring.c:20)
==6919== by 0x400AD7: main (test.c:14)
==6919==
==6919== Invalid write of size 8
==6919== at 0x400860: lgw_init_dstring (dstring.c:34)
==6919== by 0x400AD7: main (test.c:14)
==6919== Address 0x51de050 is 8 bytes after a block of size 8 alloc'd
==6919== at 0x4C28C20: malloc (vg_replace_malloc.c:296)
==6919== by 0x4007A0: lgw_init_dstring (dstring.c:20)
==6919== by 0x400AD7: main (test.c:14)
==6919==
==6919== Invalid read of size 8
==6919== at 0x400A30: lgw_append_dstring (dstring.c:87)
==6919== by 0x400B21: main (test.c:19)
==6919== Address 0x51de048 is 0 bytes after a block of size 8 alloc'd
==6919== at 0x4C28C20: malloc (vg_replace_malloc.c:296)
==6919== by 0x4007A0: lgw_init_dstring (dstring.c:20)
==6919== by 0x400AD7: main (test.c:14)
==6919==
==6919== Invalid read of size 8
==6919== at 0x40093C: lgw_write_dstring (dstring.c:65)
==6919== by 0x400A59: lgw_append_dstring (dstring.c:87)
==6919== by 0x400B21: main (test.c:19)
==6919== Address 0x51de048 is 0 bytes after a block of size 8 alloc'd
==6919== at 0x4C28C20: malloc (vg_replace_malloc.c:296)
==6919== by 0x4007A0: lgw_init_dstring (dstring.c:20)
==6919== by 0x400AD7: main (test.c:14)
==6919==
==6919== Invalid read of size 8
==6919== at 0x40096F: lgw_write_dstring (dstring.c:68)
==6919== by 0x400A59: lgw_append_dstring (dstring.c:87)
==6919== by 0x400B21: main (test.c:19)
==6919== Address 0x51de050 is 8 bytes after a block of size 8 alloc'd
==6919== at 0x4C28C20: malloc (vg_replace_malloc.c:296)
==6919== by 0x4007A0: lgw_init_dstring (dstring.c:20)
==6919== by 0x400AD7: main (test.c:14)
==6919==
==6919== Invalid write of size 8
==6919== at 0x400A11: lgw_write_dstring (dstring.c:80)
==6919== by 0x400A59: lgw_append_dstring (dstring.c:87)
==6919== by 0x400B21: main (test.c:19)
==6919== Address 0x51de048 is 0 bytes after a block of size 8 alloc'd
==6919== at 0x4C28C20: malloc (vg_replace_malloc.c:296)
==6919== by 0x4007A0: lgw_init_dstring (dstring.c:20)
==6919== by 0x400AD7: main (test.c:14)
==6919==
value is : test123
==6919==
==6919== HEAP SUMMARY:
==6919== in use at exit: 0 bytes in 0 blocks
==6919== total heap usage: 2 allocs, 2 frees, 524 bytes allocated
==6919==
==6919== All heap blocks were freed -- no leaks are possible
==6919==
==6919== For counts of detected and suppressed errors, rerun with: -v
==6919== ERROR SUMMARY: 6 errors from 6 contexts (suppressed: 0 from 0)
答案 0 :(得分：3)
为分配结构指定了错误的内存量：
if((*dstr = malloc(sizeof *dstr)) == NULL)
由于dstr是（struct dstr **），因此sizeof（* dstr）是指针的大小，而不是结构的大小。要解决这个问题，您可能希望以这种方式编写它：
if((*dstr = malloc(sizeof **dstr)) == NULL)