程序正在运行，但是测试抛出分段错误

Question

I have to create a program using linked list concept. It works on ubuntu, ideone.com, but when I submit it to the university tester, it reports Segmentation fault/Bus error/Memory limit exceeded/Stack limit exceeded (one of the list).

Probably, problem is memory deallocation because only DevCpp fall down, and it causes a piece of code where I use free.

So, I used Valgrind, but I can't understand very much, what is written in the log,but it's still writing "Invalid read of size 8" or Invalid write of size 8. And it's related to memory allocation(sizeof blocks is 8, but not always I suppose). Further there is written -"ERROR SUMMARY: 76 errors from 48 contexts (suppressed: 2 from 2)" and "total heap usage: 20 allocs, 20 frees, 160 bytes allocated" (I consider that lines important).

Finally, there is piece of likely problematic code.

TITEM *borrowItem(const char *to)
{ 
    TITEM *newItem = (TITEM *)malloc(sizeof(newItem));
    newItem->m_Next = NULL;
    newItem->m_To=(char *)malloc(sizeof(to));
    strcpy(newItem->m_To,to);
    newItem->m_Cargo = NULL;
    return newItem;
}

I suppose that problem is in allocation already. This function is used for creating of new list item pointer. Memory is freed here:

void freeItem(TITEM *item)
{
    free(item->m_To);
    free(item);     
    return;    
}

m_To is string and m_Next is next item pointer.

Answer 1

You can't copy a string like this:

newItem->m_To=(char*)malloc(sizeof(to));
strcpy(newItem->m_To,to);

The value of sizeof(to) will be the number of bytes occupied by a pointer (4 or 8).

You should either do this:

newItem->m_To = malloc(strlen(to) + 1);
strcpy(newItem->m_To,to);

Or use the library function strdup , which does essentially the same thing.

newItem->m_To = strdup(to);

Note that I also removed the cast to (char*) from the malloc call. You should also remove the cast in your other malloc call. If this is straight C, that is...

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Dipstick said: Correct but possibly incomplete. Isn't the malloc of newItem also just allocating the size of the pointer.

You should allocate your structure like this:

TITEM *newItem = malloc(sizeof(TITEM));