multiple calls to realloc() seems to cause a heap corruption
What's the problem with this code? It crashes every time.
One time it's a failed assertion "_ASSERTE(_CrtIsValidHeapPointer(pUserData));", other times it is just a "heap corrpuption" error.
Changing the buffer size affects this issue in some strange ways - sometimes it crashes on the "realloc", and other times on the "free".
I have debugged this code many times, and there is nothing abnormal regarding the pointers.
char buf[2000];
char *data = (char*)malloc(sizeof(buf));
unsigned int size = sizeof(buf);
for (unsigned int i = 0; i < 5; ++i)
{
char *ptr = data + size;
size += sizeof(buf);
char *tmp = (char*)realloc(data, size);
if (!tmp)
{
std::cout << "Oh no..";
break;
}
data = tmp;
memcpy(ptr, buf, sizeof(buf));
}
free(data);
Thanks!
You're trashing the heap. realloc can freely choose to return you memory from an entirely different location as it reallocates, and this is invalidating your ptr . Set ptr after reallocating.
On the second iteration of the loop here are the values
data points to a buffer of size sizeof(buf) size has a value of sizeof(buf) Given these values the value of ptr is that it points past the end of the buffer allocated into data . This is memory not owned by the process and the following memcpy operation writes to this and corrupts memory.
char *ptr = data + size;
char *tmp = (char*)realloc(data, size);
memcpy(ptr, buf, sizeof(buf));
这里对realloc()的调用可能会释放旧的缓冲区，然后返回新的缓冲区。
上一篇: 如果调试运行正常，该怎么办，但释放崩溃