How to call a host function in a CUDA kernel?

Question

As the following error implies, calling a host function ('rand') is not allowed in kernel, and I wonder whether there is a solution for it if I do need to do that.

error: calling a host function("rand") from a __device__/__global__ function("xS_v1_cuda") is not allowed

Answer 1

Unfortunately you can not call functions in device that are not specified with __device__ modifier. If you need in random numbers in device code look at cuda random generator curand http://developer.nvidia.com/curand

If you have your own host function that you want to call from a kernel use both the __host__ and __device__ modifiers on it:

__host__ __device__ int add( int a, int b )
{
    return a + b;
}

When this file is compiled by the NVCC compiler driver, two versions of the functions are compiled: one callable by host code and another callable by device code. And this is why this function can now be called both by host and device code.