Pointer to pointer syntax problem

Lets say I have the following:

void init_gpu(cuComplex* d_hhBuff)
{   
    cutilSafeCall(cudaMalloc((void **)&d_hhBuff, memsize));
}

and I call it with something like

cuComplex *my_buff;
init_gpu(my_buff);

Well, when init_gpu returns, it is NOT pointing to the device memory that cudaMalloc allocated.

How do I modify this so that the caller of init_gpu wil开发者_StackOverflow社区l have my_buff pointing to the modified d_hhBuff that cudaMalloc creates?

The problem is that you are passing the pointer by value. Change the function header to

void init_gpu(cuComplex *& d_hhBuff)

Your d_hhBuf is a local copy. What you should do is pass the pointer by reference:

void init_gpu(cuComplex * & d_hhBuff)

Assume you typedef:

typedef cuComplex* ComplexPointer;

And write a function:

void ChangeComplex(ComplexPointer ptr)
{
   ptr = new cuComplex;
}

And call it:

ComplexPointer cptr;
ChangeComplex(cptr);

What would you deduce by looking at call and the function (and not knowing the typedef) ? You would say, the ptr (cptr) is passed by value, and not by reference/pointer and won't change.

Now consider this call:

cuComplex* ptr;
ChangeComplex(cptr);

This is exactly same as above, you are actually passing type ComplexPointer - which just being passed by value.

Finally understand the changed signature:

void ChangeComplex(cuComplex*ptr);

And it is still the same - you are pass the type cuComplex* by VALUE, and not by reference!