cudaMemcpyToSymbol not copying data from host to constant memory

Alec Jacobson

I had declared some constant memory variable at the top of my program like this:

__device__ __constant__ float constant_T[M];

Then I tried to fill it from my host array T with the following:

cudaMemcpyToSymbol("constant_T", T, sizeof(float)*M,cudaMemcpyHostToDevice);

Surprisingly I got no compilation errors and no cuda errors at runtime via

printf("Cuda errors: %s\n", cudaGetErrorString( cudaGetLastError() ) );

After some staring I finally figured it out, the copying doesn't need the last parameter. It should be:

cudaMemcpyToSymbol("constant_T", T, sizeof(float)*M);