Output of CUDA program is empty [duplicate]

This question already has answers here: Closed 开发者_开发技巧11 years ago.

Possible Duplicate:

Output of cuda program is not what was expected

I am running this simple CUDA program:

#include <cuda_runtime.h>
#include <cuda.h>
#include <stdio.h>

__global__ void
  display(char *t[])
{

  int v = blockIdx.x;
  int p = blockIdx.y;
  int offset = v+ p*gridDim.x;
  t[offset] = "(";
  //
}

void 
main()
{
  int c = 5;
  cudaGetDeviceCount(&c);
  cudaDeviceProp prop;
  cudaGetDeviceProperties(&prop,0);
  printf("The device name is : %s\n", prop.name);
  //bool value = prop.integrated;
  char *x[6];
  int i;
  for (i = 0; i<6; i++)
      cudaMalloc((void**)&x[i], 20*sizeof(char));

  // Checking the meaning of grid(3,2)
  dim3 grid(3,2); 
  display<<<grid,1>>>(x);
  char y[30];
  cudaMemcpy(y, x[0], 20*sizeof(char), cudaMemcpyDeviceToHost);
  printf("The values is :%s\n", y);
  cudaFree(x[0]);

  getchar();
}

I don't understand why the array y is still empty at the end of the execution. Shouldn't it be "("?

---

I've answered this question here.

But I'll leave this suggestion to others who land on this question first:

In debugging CUDA code, I strongly recommend adding in a forced synchronization and check for errors, as I mentioned in your other post to ensure that your hardware setup, API setup, current weather, aren't messing things up:

/*  Force Thread Synchronization  */
cudaError err = cudaThreadSynchronize();

/*  Check for and display Error  */
if ( cudaSuccess != err )
{
    fprintf( stderr, "Cuda error in file '%s' in line %i : %s.\n",
             __FILE__, __LINE__, cudaGetErrorString( err) );
}

The key problem with the OP's code is that x lives on the CPU even though it's members live on the GPU. Again, see my answer here.