线程1：EXC_BAD_ACCESS（code = 2，address = 0x8）错误c ++

Question

I'm developing c++ application . I have allocated memory but im getting the Error Thread 1: EXC_BAD_ACCESS ( code=2,address=0x8) in superfile.cpp. Here is my code :

superfile.h

struct Node{
        Voxel   *data;
        Node    *next;
    };

superfile.cpp

int* cnt =(int*)calloc(_width*_height,sizeof(int));
    Voxel *temp =(Voxel *)calloc(_width*_height,sizeof(Voxel)); 
    Node *list=(Node *)calloc(_width*_height*2,sizeof(Node));

list[(_width*_height)+l].next = list[_width*yy + xx].next->next; // Thread 1: EXC_BAD_ACCESS ( code=2,address=0x8) Error c++

after debugging the values of the variables are:

_width=60
_height=45
l=3
yy=4096
xx=-3345

Any idea what is going on ? Thank you

Answer 1

You're allocating not enough memory. Here, the size of list is 60*45*2=5400 elements. You're trying to access the 60*4096-3345=242415th element.

That's access to memory that doesn't belong to the memory associated with list . The 242415th element doesn't exist . That's SegmentationFault.

You'll need to use something like calloc(_width*_height*100,sizeof(...)); to handle this. However, you'll waste lots of memory then.

Also, you never allocate memory for next and next->next . Try this

list[_width*yy + xx].next=calloc(50, sizeof(...));
list[_width*yy + xx].next->next=calloc(50, sizeof(...));
list[(_width*_height)+l].next = list[_width*yy + xx].next->next;

Here 50 is just random number, I'm not sure how much space does your struct consume.

Answer 2

You're dereferencing a null pointer here:

list[(_width*_height)+l].next = list[_width*yy + xx].next->next;
                                                         ^^^^^^

The value at list[_width*yy + xx].next is 0 , as initialized by calloc .