How to allocate Dynamic Memory to Device Pointer variable in C++ CUDA

all programmers. I'm converting the existing C++ project to CUDA enhanced program. I'm new to CUDA. So I'm learning during work. I have to allocate memory to a dynamic struct member variable and the struct variable is allocated as device variable.

like this:

_cuda_params* dcuda_params;

cudaMalloc(&dcuda_params, sizeof(_cuda_params));

cudaMemcpy((void *)dcuda_params, (void*)cuda_params, sizeof(_cuda_params), cudaMemcpyHostToDevice);

dcuda_params->DPht = (hashtb_entry *)malloc(c);  // c is size to allocate.

But during run time I get Exception 0xC0000022. I also tried this:

cudaMalloc(&dcuda_params->DPht, c);

but the result is the same. How can I handle this?

.h file
    typedef struct {
        int blocksPerGrid;
        int threadsPerBlock;
        uint64_t HASH_SIZE;
        hashtb_entry* DPht;
    } _cuda_params;

.cu file

void _GpuSearch(_cuda_params* cuda_params){
...
        _cuda_params* dcuda_params;
        cudaMalloc(&dcuda_params, sizeof(_cuda_params));
        cudaMemcpy((void *)dcuda_params, (void*)cuda_params, sizeof(_cuda_params), 
        cudaMemcpyHostToDevice);
        dcuda_params->DPht = (hashtb_entry *)malloc(c); //c: size to allocate.
...
}

You are dereferencing a device pointer, dcuda_params->DPht = (hashtb_entry *)malloc(c); it is not allowed as the host doesn't have access to device memory.

The easy solution for your problem would be not using a pointer to an instance of your struct. You are not using an array of it anyway. So the function call changes to:

void _GpuSearch(_cuda_params cuda_params)

let's say cuda_params is not a pointer anymore you can simply do:

cudaMalloc(&cuda_params.DPht , sizeof(hashtb_entry));

from now on you are fine to pass cuda_params by value to the kernel. And if needed you copy from host to cuda_params.DPht.