nvlink error : Undefined reference to variables

Accelerated Computing CUDA CUDA Programming and Performance
1

kernel.h

.
.
/* constant variables deceleration */

extern __constant__ uint8_t var1;
extern __constant__ uint8_t var2;
extern __constant__ uint8_t var3;
extern __constant__ uint8_t var4;

_global__ void MyKernel(blah,blah...);
.
.

kernel.cu
_

#include "kernel.h"

_global__ void MyKernel(blah,blah...){

// Here i am using var1,var2,var3,var4
.
.
}

main.cu

{

#include "kernel.h"

.
.
cudaMemcpyToSymbol(var1,...)
cudaMemcpyToSymbol(var2,...)
cudaMemcpyToSymbol(var3,...)
cudaMemcpyToSymbol(var4,...)

/* Call kernel */

MyKernel <<<....>>>
.
.
}

Cuda Separable compilation is ON.

nvcc prompt the linking error for var1,var2,var3,var4 (i.e. undefined reference)

2

You have no definition for those variables. The statement marked with extern does not define the variable.

Perhaps you don’t understand how extern is used in C++

The first answer here may be useful:

[url]variable declaration - When to use extern in C++ - Stack Overflow

3

Thank you.

I haven’t defined the variables at the file scope in main.cu.