realloc() 内存泄漏

Question

我有一个向字符串添加字符的函数：

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 表明该行： (*str)=realloc(*str, len+2) 正在泄漏内存。 这是 realloc 的实现问题吗？ 还是我使用不当？

这是 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

谢谢。

Answer 1

您的仪器是否表明存在实际泄漏或潜在泄漏？

如果realloc()失败，像您一样使用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。 因此，您将丢失指向该块的指针并且无法释放它（除非该指针存储在其他地方）。

但这应该很少发生（即，当您耗尽内存时）。

如果这就是您的工具所抱怨的，您应该能够使用以下内容修复泄漏警告：

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。 您应该确保在不再需要重新分配的字符串后，将其释放为 free 。

Answer 3

我不知道有关realloc实现问题，但此代码中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； 它不会被释放或移动。

并且，由于realloc在失败时返回NULL ，如果失败，您将丢失指向已分配内存块的唯一指针，因此您会发生内存泄漏。

为了避免这个问题，你应该这样做：

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'; }