realloc（）泄漏内存

Question

我有一个函数可以在字符串中添加一个字符：

void AddChToString(char **str,char ch){
    int len=(*str)?strlen(*str):0;
    (*str)=realloc(*str, len+2);
    (*str)[len]=ch;
    (*str)[len+1]='\0';
}

仪器（在mac上）和Valgrind表示行：（* str）= realloc（* str，len + 2）正在泄漏内存。这是realloc的实现问题吗？或者我使用不当？

以下是Valgrind的输出：

==39230== 6 bytes in 1 blocks are definitely lost in loss record 1 of 7
==39230==    at 0x100018B2D: realloc (vg_replace_malloc.c:525)
==39230==    by 0x100002259: AddChToString (in ./OpenOtter)
==39230==    by 0x10000477B: QueryMapFromString (in ./OpenOtter)
==39230==    by 0x100684CD2: ???
==39230==    by 0x100001FB0: RequestHandler (in ./OpenOtter)
==39230==    by 0x100065535: _pthread_start (in /usr/lib/libSystem.B.dylib)
==39230==    by 0x1000653E8: thread_start (in /usr/lib/libSystem.B.dylib)
==39230== 
==39230== 9 bytes in 1 blocks are definitely lost in loss record 2 of 7
==39230==    at 0x100018B2D: realloc (vg_replace_malloc.c:525)
==39230==    by 0x100002259: AddChToString (in ./OpenOtter)
==39230==    by 0x10000298E: ParseHTTPRequest (in ./OpenOtter)
==39230==    by 0x100004151: OpenRoutesFile (in ./OpenOtter)
==39230==    by 0x10000142B: main (in ./OpenOtter)
==39230== 
==39230== 45 bytes in 5 blocks are definitely lost in loss record 3 of 7
==39230==    at 0x100018B2D: realloc (vg_replace_malloc.c:525)
==39230==    by 0x100002259: AddChToString (in ./OpenOtter)
==39230==    by 0x10000298E: ParseHTTPRequest (in ./OpenOtter)
==39230==    by 0x100001EB4: RequestHandler (in ./OpenOtter)
==39230==    by 0x100065535: _pthread_start (in /usr/lib/libSystem.B.dylib)
==39230==    by 0x1000653E8: thread_start (in /usr/lib/libSystem.B.dylib)
==39230== 
==39230== LEAK SUMMARY:
==39230==    definitely lost: 60 bytes in 7 blocks
==39230==    indirectly lost: 0 bytes in 0 blocks
==39230==      possibly lost: 0 bytes in 0 blocks
==39230==    still reachable: 1,440 bytes in 4 blocks
==39230==         suppressed: 0 bytes in 0 blocks

感谢。

Answer 1

您的仪器是否表明存在实际泄漏或存在潜在泄漏？

如果 realloc()失败，那么使用realloc()会泄漏内存。在这种情况下，它将返回NULL但不会释放原始块。所以你将失去指向该块的指针并且无法释放它（除非指针存储在别处）。

但这应该是罕见的（即，当你耗尽记忆力时）。

如果这是您的工具所抱怨的，您应该能够通过以下方式修复泄漏警告：

void AddChToString(char **str,char ch){
    int len=(*str)?strlen(*str):0;
    char* tmp = realloc(*str, len+2);

    if (!tmp) {
        // whatever error handling is appropriate
    }

    (*str)=tmp;
    (*str)[len]=ch;
    (*str)[len+1]='\0';
}

Answer 2

调用realloc本身不会泄漏内存。您应该确保重新分配的字符串的内存在不再需要时免费释放。

Answer 3

我不知道有关realloc的实施问题，但此代码肯定有内存泄漏的机会：来自realloc联机帮助页：

  

如果 realloc() 失败，则原始块保持不变;它没有被释放或移动。

并且，因为realloc在失败时返回NULL，如果失败，则会丢失指向已分配的内存块的唯一指针，因此存在内存泄漏。

为避免此问题，您应该：

char * temp=realloc(*str, len+2);
if(temp==NULL)
{
    /* handle the error in some way */
}
else
    *str=temp;

Answer 4

尝试使用单独的变量重新分配，然后调用strcpy将str变量放入该空间，如下所示：

void AddChToString(char **str,char ch){
char *blah;
int len=(*str)?strlen(*str):0;
blah=realloc(NULL, len+2);
strcpy(blah, str); 
(*str)[len]=ch;   
(*str)[len+1]='\0'; }