c++ - CUDA 5.5 cudaMemcpyToSymbol, __constant__ and out of scope error

Question

I'm trying to compile a CUDA example which has;

cuda.cu:

__constant__ unsigned VERTICES;
__constant__ unsigned TRIANGLES;

and the corresponding code in main.cpp;

cudaMemcpyToSymbol(VERTICES, &verticesNo, sizeof(int));
cudaMemcpyToSymbol(TRIANGLES, &trianglesNo, sizeof(int));

How to avoid "VERTICES not declared in this scope" error when compiling the main.cpp?

TIA.

cheers,

Answer 1

CUDA __constant__ variables have a file scope linkage. That means that the cudaMemcpyToSymbol have to be in the same .cu file where the __constant__ variable is defined.

You can add a wrapper function to the .cu file and call this one from your .cpp file.

sample for cuda.cu:

__constant__ unsigned VERTICES;
__constant__ unsigned TRIANGLES;

void wrapper_fn(unsigned *verticesNo, unsigned *trianglesNo)
{
  cudaMemcpyToSymbol(VERTICES, verticesNo, sizeof(unsigned));
  cudaMemcpyToSymbol(TRIANGLES, trianglesNo, sizeof(unsigned));
}

Then only call wrapper_fn in your main.cpp.