realloc pointer change when out of function

Question

i am starting homework about dynamic array, first, I have a 2 dimensional array :

int initializeInfo[3][4] ={{77,68,0,0},{96,87,89,78},{70,90,86,0}};

and use pointer to store it:

int **ptr = (int**)malloc(3*sizeof(int));
int size = 0;
for(int i =0;i<3;i++){
    addInitiazeInfo(ptr,initializeInfo[i],size);
}

here is function addInitiazeInfo:

void addInitiazeInfo(int**& ptr, int arr[],int& size){
    ptr[size] = (int*)malloc(4*sizeof(int));
    if(ptr[size] == NULL){
        return;
    }
    ptr[size] = arr;
    size++;
}

It's run OK! The 2 dimensional array is store by ptr pointer. enter image description here

And I want to add new row, I think realloc is needed, then I try:

int arr[] = {3,4,5,6};
size++;            
ptr = (int**)realloc(ptr,size * sizeof( int ) );
ptr[size-1] = (int*)malloc(4*sizeof(int));
ptr[size-1] = arr;

But I think this is my trouble, the output make me hard to know how it happend: enter image description here

please help me, thanks everyone

int **ptr = (int**)malloc(3*sizeof(int)); is wrong (and so is the realloc)) . BTW: C does not have references. Maybe you mean C++ ? — wildplasser
– wildplasser, Commented Jun 26, 2013 at 9:02
The defined type for ptr is int **ptr;, so it points to a pointer, (or to the first member of an array of pointers) So, you should allocate 3 * sizeof (int*) chars for it. AND: mixing C and C++ really is a bad habit. — wildplasser
– wildplasser, Commented Jun 26, 2013 at 9:15
When your program contains **& it doesn't matter whether you make it work or not, your program is unreadable either way. — Sebastian Redl
– Sebastian Redl, Commented Jun 26, 2013 at 9:43

Karthik T · Accepted Answer · 2013-06-26 09:04:35Z

2

When you do

ptr[size] = arr;

You are essentially assigning the address of arr, to ptr[size]. This means that the memory you just allocated is lost and successfully leaked.

You want to manually copy element by element or use something like memcpy. It is likely this might fix your issue, depending on the rest of your code.

answered Jun 26, 2013 at 9:04

Karthik T

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