CUDA C++第一个项目“Hello World”

#include <iostream>
#include <cmath>

// Kernel function to add the elements of two arrays
__global__ void add(int n, float *x, float *y) {
    int index = blockIdx.x * blockDim.x + threadIdx.x;
    int stride = blockDim.x * gridDim.x;
    for (int i = index; i < n; i += stride) y[i] = x[i] + y[i];
}

int main() {
    int N = 1 << 20;
    float *x, *y;

    // Allocate Unified Memory – accessible from CPU or GPU
    cudaMallocManaged(&x, N * sizeof(float));
    cudaMallocManaged(&y, N * sizeof(float));
    // initialize x and y arrays on the host
    for (int i = 0; i < N; i++) {
        x[i] = 1.0f;
        y[i] = 2.0f;
    }

    // Run kernel on 1M elements on the GPU
    add<<<1, 1>>>(N, x, y);
    // Wait for GPU to finish before accessing on host
    cudaDeviceSynchronize();

    // Check for errors (all values should be 3.0f)
    float maxError = 0.0f;
    for (int i = 0; i < N; i++) maxError = fmax(maxError, fabs(y[i] - 3.0f));
    std::cout << "Max error: " << maxError << std::endl;

    // Free memory
    cudaFree(x);
    cudaFree(y);
    return 0;
}