CUDA COnstant memory use

Question

I have a cuda project containing the following files

Header File:

 Declarations.h

Main File:

 main.cpp:
    #include "Declarations.h"

And Kernel File:

Kernel.cu:
    #include "Declarations.h"

In main.cpp, I have float K1[3*3] which I want to copy to GPU constant memory. To do so, I declared __constant__ float K1_d[3*3];in Declarations.h and In main.cpp I did

checkCudaErrors( cudaMemcpyToSymbol(&K1_d, &K1, 9*sizeof(float)) );

When running the code I got the following error: CUDA error at c:\users\xxx\test.cpp:241 code=13(cudaErrorInvalidSymbol) "cudaMemcpyToSymbol(&K1, &K1_inv, 9*sizeof(float))"

I tried to copy one variable, for example, I declared in the header file

__constant__ float N;

And did:checkCudaErrors( cudaMemcpyToSymbol(&N, &K1_inv[0], sizeof(float)) );

I got the same error message of the macro chechCudaErrors.

How to transer variables to constant memory in CUDA?`