constant memory

Question

I write code for copying an integer to constant memory and use it in a global function,but it doesn't work correctly.I mean that no "cuPrintf" in global function works and nothing printed!

I think it is because of "if(*num == 5)",since I remove it, all "cuPrintf" print what I want!

I also try "if(num == 5)" but my visual studio doesn't compile it and shows error.

why "num" is correct in "cuPrintf" but it is not correct in "if" statement?

how should I use "num" in an "if" statement?

#include "cuda_runtime.h"
#include "device_launch_parameters.h"

#include "stdio.h"
#include "stdlib.h"
#include "cuPrintf.cu"

__constant__ int* num;

__global__ void kernel(){
cuPrintf("\n num=%d\n",num);
if(*num == 5)
    cuPrintf("\n num is equal 5");
else
    cuPrintf("\n num is not equal 5");
}

void main(){    
int x;
printf("\n\nPlease enter x:");
scanf("%d",&x);
cudaMemcpyToSymbol( num, &x,sizeof(int)*1);

cudaPrintfInit();
kernel<<<1,1>>>();
cudaPrintfDisplay(stdout, true);
cudaPrintfEnd();

int wait;
scanf("%d",&wait);
}

if I change:

__constant__ int* num;

to

__constant__ int num;

and also change:

cudaMemcpyToSymbol( num, &x,sizeof(int)*1);

to

cudaMemcpyToSymbol( &num, &x,sizeof(int)*1);

then

cuPrintf("\n num=%d\n",num);

will show "num=0" with any input!

Answer 1

"num" should not be a pointer. I changed your code to the one below, works for me (note it requires SM 2.0 or newer for printf):

#include "cuda_runtime.h"
#include "device_launch_parameters.h"

#include "stdio.h"
#include "stdlib.h"

__constant__ int num;

__global__ void kernel() {
    printf("\n num=%d\n", num);
    if (num == 5)
        printf("\n num is equal 5");
    else
        printf("\n num is not equal 5");
}

int main() {
    cudaError_t err;
    int x;
    printf("\n\nPlease enter x:");
    scanf("%d", &x);
    err = cudaMemcpyToSymbol(num, &x, sizeof(int) * 1);
    if (err != cudaSuccess) {
        printf("Error: %d\n", err);
        return 1;
    }

    kernel<<<1, 1>>>();
    err = cudaDeviceSynchronize();
    if (err != cudaSuccess) {
        printf("Error: %d\n", err);
        return 1;
    }
    return 0;
}