Alexander M Alexander M - 2 months ago 12x
C Question

adding two numbers CUDA

I am learning CUDA and need some help.
Here is my program from NVIDIA's presentation:

__global__ void add(int *a, int *b, int *c)
*c = *a + *b;

int main(void) {
int a, b, c; // host copies of a, b, c
int *d_a, *d_b, *d_c; // device copies of a, b, c
int size = sizeof(int);

// Allocate space for device copies of a, b, c
cudaMalloc((void **)&d_a, size);
cudaMalloc((void **)&d_b, size);
cudaMalloc((void **)&d_c, size);

// Setup input values
a = 2;
b = 7;

// © NVIDIA Corporation 2011
// Addition on the Device: main()
// Copy inputs to device
cudaMemcpy(d_a, &a, size, cudaMemcpyHostToDevice);
cudaMemcpy(d_b, &b, size, cudaMemcpyHostToDevice);

// Launch add() kernel on GPU
add<<<1,1>>>(d_a, d_b, d_c);

// Copy result back to host
cudaMemcpy(&c, d_c, size, cudaMemcpyDeviceToHost);

// Cleanup
cudaFree(d_a); cudaFree(d_b); cudaFree(d_c);

return 0;

Each time I run this code the value of
is not 9.
How to get real value of



printf("%d", c);

instead of

printf("%d", &c);

as currently you are printing the address of the local var c instead of its value