I am trying to copy a struct array to device.I am working with one

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Asked: May 23, 20262026-05-23T13:55:29+00:00 2026-05-23T13:55:29+00:00

I am trying to copy a struct array to device.I am working with one

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I am trying to copy a struct array to device.I am working with one GPU atm, and i have a problem with cuPrintf function which i use to debug my code.

My struct definition is as below:

 struct Node
 {
        char Key[25];
        char ConsAlterKey[25];
        char MasterKey[3];
        int VowelDeletion;
        char Data[6];
        char MasterData[6];
        int Children[35];
        int ChildCount;
 };

and for test purpose i fill the struct array like this :

void FillArray(Node *NodeArray)
{       
    for(int i=0;i<TotalNodeCount;i++)
    {
            strcpy(NodeArray[i].Key,"Key");

            strcpy(NodeArray[i].ConsAlterKey,"ConsAlterKey");

            strcpy(NodeArray[i].MasterKey,"Mk");

            NodeArray[i].VowelDeletion=0;

            strcpy(NodeArray[i].Data,"Data");

            strcpy(NodeArray[i].MasterData,"Mdata");

            NodeArray[i].ChildCount=5;

            for(int j =0;j<NodeArray[i].ChildCount;j++)
            {
                    NodeArray[i].Children[j]=i+j;
            }
    }
}

my main function looks like this:

int main()
{
    Node *NodeArray;
    Node *GpuTree;
    int tokenCount=0;
    int *tokenCountGPU;

    NodeArray =(Node *)malloc(sizeof(Node)*(TotalNodeCount));
    FillArray(NodeArray);
    printf("Filling test : %s\n", NodeArray[13].Key);

    gpuAssert(cudaMalloc( (void**)&GpuTree, sizeof(Node)*(TotalNodeCount)));
    gpuAssert(cudaMemcpy(GpuTree, NodeArray,sizeof(Node)*(TotalNodeCount), cudaMemcpyHostToDevice));

    //test value
    tokenCount=35;


    gpuAssert( cudaMalloc((void **)&tokenCountGPU, sizeof(int)) );
    gpuAssert( cudaMemcpy(tokenCountGPU, &tokenCount, sizeof(int), cudaMemcpyHostToDevice) );

    cudaPrintfInit();
    Test <<< 1, tokenCount >>> (GpuTree,tokenCountGPU);
    cudaPrintfDisplay(stdout, true);
    cudaPrintfEnd();
    gpuAssert( cudaGetLastError() );

    //TODO:free pointers
    return(0);
}

and if I write test function as below:

__global__ void Test(Node *Trie,int *tokenCount)
{
    if (threadIdx.x < *tokenCount) 
    {
            cuPrintf("%s\n",Trie[threadIdx.x].Key);

    }   
    return;
}

i get output like this:

Filling test : Key
[0, 0]: <
[0, 1]: ¶☺!
[0, 2]: ì☺!
[0, 3]: Ä☻!
[0, 4]: o♥!
[0, 5]: t♦!
[0, 6]: L♣!
[0, 7]: $♠!
[0, 8]: ü♠!
[0, 9]: Ô!
[0, 10]: !
[0, 11]: "
[0, 12]: \
!
[0, 13]: 4♂!
[0, 14]: ♀♀!
[0, 15]: ä♀!
!0, 16]: ¼
[0, 17]: "♫!
[0, 18]: l☼!
[0, 19]: D►!
[0, 20]: ∟◄!
[0, 21]: ô◄!
[0, 22]: Ì↕!
[0, 23]: ¤‼!
[0, 24]: |¶!
[0, 25]: T§!
[0, 26]: ,▬!
[0, 27]: ♦↨!
[0, 28]: Ü↨!
[0, 29]: ´↑!
[0, 30]: O↓!
[0, 31]: d→!
[0, 32]: <←!
[0, 33]: ¶∟!
[0, 34]: ì∟!

but if i change my test method to this:

__global__ void Test(Node *Trie,int *tokenCount)
{
    if (threadIdx.x < *tokenCount) 
    {
        cuPrintf("%c%c%c\n",
                            Trie[threadIdx.x].Key[0],
                            Trie[threadIdx.x].Key[1],
                            Trie[threadIdx.x].Key[2]);
    }
    return;
}

then i get the correct output:

Filling test : Key
[0, 0]: Key
[0, 1]: Key
[0, 2]: Key
[0, 3]: Key
[0, 4]: Key
[0, 5]: Key
[0, 6]: Key
[0, 7]: Key
[0, 8]: Key
[0, 9]: Key
[0, 10]: Key
[0, 11]: Key
[0, 12]: Key
[0, 13]: Key
[0, 14]: Key
[0, 15]: Key
[0, 16]: Key
[0, 17]: Key
[0, 18]: Key
[0, 19]: Key
[0, 20]: Key
[0, 21]: Key
[0, 22]: Key
[0, 23]: Key
[0, 24]: Key
[0, 25]: Key
[0, 26]: Key
[0, 27]: Key
[0, 28]: Key
[0, 29]: Key
[0, 30]: Key
[0, 31]: Key
[0, 32]: Key
[0, 33]: Key
[0, 34]: Key

So the question is why do i get corrupt output when I try to print strings through using “%s”?

So the problem is solved.Looks like it is because of cuPrintf limitations. And actually i was not aware of them.Thank you.

Here is a small test:

__global__ void Test(Node *Trie,int *tokenCount)
{
    const char *Key="Key";
    char *KeyPointer="Key";
    char KeyArray[4]="Key";
    cuPrintf("Constant : %s - Array :%s  - Pointer : %s - Casting Pointer : %s - Casting Array : %s\n",Key, KeyArray,KeyPointer,(const char *)KeyPointer,(const char *)KeyArray);

    //cuPrintf("%s\n",Trie[threadIdx.x].Key);
    //cuPrintf("%d\n",*tokenCount);

}

Gives the output :

    [0, 0]: Constant : Key - Array :  - Pointer : ♀ - Casting Pointer : Key - Casting Array : Key
    [0, 1]: Constant : Key - Array :  - Pointer : ♀ - Casting Pointer : Key - Casting Array : Key
    [0, 2]: Constant : Key - Array :  - Pointer : ♀ - Casting Pointer : Key - Casting Array : Key
    [0, 3]: Constant : Key - Array :  - Pointer : ♀ - Casting Pointer : Key - Casting Array : Key
    [0, 4]: Constant : Key - Array :  - Pointer : ♀ - Casting Pointer : Key - Casting Array : Key
    [0, 5]: Constant : Key - Array :  - Pointer : ♀ - Casting Pointer : Key - Casting Array : Key
    [0, 6]: Constant : Key - Array :  - Pointer : ♀ - Casting Pointer : Key - Casting Array : Key
    [0, 7]: Constant : Key - Array :  - Pointer : ♀ - Casting Pointer : Key - Casting Array : Key
    [0, 8]: Constant : Key - Array :  - Pointer : ♀ - Casting Pointer : Key - Casting Array : Key
    [0, 9]: Constant : Key - Array :  - Pointer : ♀ - Casting Pointer : Key - Casting Array : Key
    [0, 10]: Constant : Key - Array :  - Pointer : ♀ - Casting Pointer : Key - Casting Array : Key
    [0, 11]: Constant : Key - Array :  - Pointer : ♀ - Casting Pointer : Key - Casting Array : Key
    [0, 12]: Constant : Key - Array :  - Pointer : ♀ - Casting Pointer : Key - Casting Array : Key
    [0, 13]: Constant : Key - Array :  - Pointer : ♀ - Casting Pointer : Key - Casting Array : Key
    [0, 14]: Constant : Key - Array :  - Pointer : ♀ - Casting Pointer : Key - Casting Array : Key
    [0, 15]: Constant : Key - Array :  - Pointer : ♀ - Casting Pointer : Key - Casting Array : Key
    [0, 16]: Constant : Key - Array :  - Pointer : ♀ - Casting Pointer : Key - Casting Array : Key
    [0, 17]: Constant : Key - Array :  - Pointer : ♀ - Casting Pointer : Key - Casting Array : Key
    [0, 18]: Constant : Key - Array :  - Pointer : ♀ - Casting Pointer : Key - Casting Array : Key
    [0, 19]: Constant : Key - Array :  - Pointer : ♀ - Casting Pointer : Key - Casting Array : Key
    [0, 20]: Constant : Key - Array :  - Pointer : ♀ - Casting Pointer : Key - Casting Array : Key
    [0, 21]: Constant : Key - Array :  - Pointer : ♀ - Casting Pointer : Key - Casting Array : Key
    [0, 22]: Constant : Key - Array :  - Pointer : ♀ - Casting Pointer : Key - Casting Array : Key
    [0, 23]: Constant : Key - Array :  - Pointer : ♀ - Casting Pointer : Key - Casting Array : Key
    [0, 24]: Constant : Key - Array :  - Pointer : ♀ - Casting Pointer : Key - Casting Array : Key
    [0, 25]: Constant : Key - Array :  - Pointer : ♀ - Casting Pointer : Key - Casting Array : Key
    [0, 26]: Constant : Key - Array :  - Pointer : ♀ - Casting Pointer : Key - Casting Array : Key
    [0, 27]: Constant : Key - Array :  - Pointer : ♀ - Casting Pointer : Key - Casting Array : Key
    [0, 28]: Constant : Key - Array :  - Pointer : ♀ - Casting Pointer : Key - Casting Array : Key
    [0, 29]: Constant : Key - Array :  - Pointer : ♀ - Casting Pointer : Key - Casting Array : Key
    [0, 30]: Constant : Key - Array :  - Pointer : ♀ - Casting Pointer : Key - Casting Array : Key
    [0, 31]: Constant : Key - Array :  - Pointer : ♀ - Casting Pointer : Key - Casting Array : Key
    [0, 32]: Constant : Key - Array :  - Pointer : ♀ - Casting Pointer : Key - Casting Array : Key
    [0, 33]: Constant : Key - Array :  - Pointer : ♀ - Casting Pointer : Key - Casting Array : Key
    [0, 34]: Constant : Key - Array :  - Pointer : ♀ - Casting Pointer : Key - Casting Array : Key

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1 Answer

Editorial Team · Answer 1 · 2026-05-23T13:55:30+00:00

Have a look at cuPrintf documentation (a readme is located at C/src/simplePrintf/doc/cuPrintf_readme.htm from the base directory where you installed the SDK):

There are Limitations/Known Issues on the usage of cuPrintf, number 2 answers your question:

Limitations / Known Issues

Currently, the following limitations
and restrictions apply to cuPrintf:

Buffer size is rounded up to the nearest factor of 256

Arguments associated with “%s” string format specifiers must be of
type (const char *)

To print the value of a (const char *) pointer, it must first be
converted to (char *). All (const char
*) arguments are interpreted as strings

Non-zero return code does not match standard C printf()

Cannot asynchronously output the printf buffer (i.e. while kernel is
running)

Calling cudaPrintfDisplay implicitly issues a
cudaDeviceSynchronize()

Restrictions applied by cuPrintfRestrict persist between
launches. To clear these from the
host-side, you must call
cudaPrintfEnd() then cudaPrintfInit()
again

cuPrintf output is undefined if multiple modules are loaded into a
single context

Compile with “-arch=sm_11” or better when possible. Buffer usage is
far more efficient and register use is
lower

Supported format specifiers are: “cdiouxXeEfgGaAs”

Behaviour of format specifiers, especially justification/size
specifiers, are dependent on the host
machine’s implementation of printf

cuPrintf requires applications to be built using the CUDA runtime API

In your case you’re not using const char* arguments.

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