# Unknown error trying to cudaFree array of pointers

**URL:** <https://forums.developer.nvidia.com/t/unknown-error-trying-to-cudafree-array-of-pointers/11713>\
**Category:** CUDA Programming and Performance\
**Created:** [August 19, 2009, 8:12pm UTC](https://forums.developer.nvidia.com/t/unknown-error-trying-to-cudafree-array-of-pointers/11713 "2009-08-19T20:12:27Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![XenoByte](https://developer.download.nvidia.com/images/forums/profile-default-devtalk-84.png) [@XenoByte](https://forums.developer.nvidia.com/u/XenoByte)\
**Post date:** [August 19, 2009, 8:12pm UTC](https://forums.developer.nvidia.com/t/unknown-error-trying-to-cudafree-array-of-pointers/11713/1 "2009-08-19T20:12:27Z")

</div>

I looked carefully at Sarnath’s recent discussion of using arrays of pointers which made perfect sense to me before I made this post but for some reason cudaFree in the following code is returning “unknown error”. This is simple code that just zeros out an array of float arrays. I feel like I must be missing something simple but I don’t see why cudaFree is complaining. The code throws no other errors and of course it runs fine with emulation.

Thanks for any help.

- Richard

```auto
[Host code]

extern "C" void ciZeroFloat( float *arrays[], int numArrays, int size ) {

	const int xBlockDim = 128;

	const int yBlockDim = 1;

	int yGridBlocks = numArrays;

	int xGridBlocks;

	cudaStream_t thisStream;

	cudaStreamCreate( &thisStream );

	dim3 dimBlock(xBlockDim,yBlockDim);

	if (size % xBlockDim == 0) xGridBlocks = (size)/xBlockDim;

	else xGridBlocks = (size)/xBlockDim + 1;

	dim3 dimGrid(xGridBlocks,yGridBlocks);

	float** d_fPtrArray;

	cutilSafeCall( cudaMalloc( (void**) &d_fPtrArray, numArrays*sizeof( float* ) ) );

	for (int i=0; i<numArrays; i++) d_fPtrArray[i] = arrays[i];

	kZeroFloat<<< dimGrid, dimBlock, 0, thisStream >>> ( d_fPtrArray, numArrays, size );

	cutilSafeCall( cudaStreamDestroy(thisStream) );

	cutilSafeCall( cudaFree( d_fPtrArray ) ); // returns -- unknown error

}

[Device code]

__global__ void 

kZeroFloat( float *arrays[], int numArrays, int size ) {

	int ndx = threadIdx.x + __mul24(blockIdx.x,blockDim.x);

	int arrNum = blockIdx.y;

	

			   __syncthreads(); // no change with our without__syncthreads()

	if (blockIdx.y < numArrays && ndx < size) {

		arrays[blockIdx.y][ndx] = 0.0f;

	}

}

```

---

<div class="post-metadata">

**Author:** ![MarkRoulo](https://developer.download.nvidia.com/images/forums/profile-default-devtalk-84.png) [@MarkRoulo](https://forums.developer.nvidia.com/u/MarkRoulo)\
**Post date:** [August 19, 2009, 10:08pm UTC](https://forums.developer.nvidia.com/t/unknown-error-trying-to-cudafree-array-of-pointers/11713/2 "2009-08-19T22:08:16Z")

</div>

The problem is probably here:

```auto
float** d_fPtrArray;

	cutilSafeCall( cudaMalloc( (void**) &d_fPtrArray, numArrays*sizeof( float* ) ) );

	for (int i=0; i<numArrays; i++) d_fPtrArray[i] = arrays[i];

```

cudaMalloc() allocates memory on the GPU.

The for loop right below it executes on the Host.

Mixing like this is not good :-)

-Mark Roulo

---

<div class="post-metadata">

**Author:** ![XenoByte](https://developer.download.nvidia.com/images/forums/profile-default-devtalk-84.png) [@XenoByte](https://forums.developer.nvidia.com/u/XenoByte)\
**Post date:** [August 20, 2009, 1:04pm UTC](https://forums.developer.nvidia.com/t/unknown-error-trying-to-cudafree-array-of-pointers/11713/3 "2009-08-20T13:04:10Z")

</div>

> [@](#):
>
> The problem is probably here:
> 
> ```auto
> float** d_fPtrArray;
> 
> cutilSafeCall( cudaMalloc( (void**) &d_fPtrArray, numArrays*sizeof( float* ) ) );
> 
> for (int i=0; i<numArrays; i++) d_fPtrArray[i] = arrays[i];
> 
> ```
> 
> cudaMalloc() allocates memory on the GPU.
> 
> The for loop right below it executes on the Host.
> 
> Mixing like this is not good :-)
> 
> -Mark Roulo

Thank you Mark, you’re absolutely right, can’t believe I missed that. Clearly I am indexing into my device array from the host and the following code seems to have fixed the problem.

```auto
cutilSafeCall( cudaMemcpy( d_fPtrArray, arrays, numArrays*sizeof( float* ), cudaMemcpyHostToDevice) );

```

Sorry to post for such a simple problem but sometimes a second set of eyes can be so incredibly helpful, especially if you’re a CUDA newbie and the only CUDA guy on the project. Thanks so much.

- R