Question

I’ve tried to allocate a memory this way:

main:

X** a;
func(a);

func:

func(X** a){
   int size = 5;
   X* array = (X*)malloc(5*sizeof(X));
   //some writing to the array..
   a = &array;
}

If using the debugger I see that when I am in the function func everything is okay = i can write to the array and a really points to the array but the moment I am back to the main I something changes and I can’t access the array through a (on the debugger it writes something like: Target request failed: Cannot access memory at address 0x909090c3 and so on).

Where is my mistake?

Note: It does compile but has a run-time problem if trying to access (print for example) the array in the main section.

Thanks.

Answer 1

You’re setting the local pointer a to the address of the local pointer array, when you want to set the target of a to the value of array:

*a = array;

and call it as

X * a;
func(&a);

It would be less confusing to return the pointer (i.e. X * func()).

Also, you’ve tagged this C++ not C, so you shouldn’t be using malloc; use the standard containers, or if they don’t work for you, allocate using new and manage the memory with a smart pointer.