为什么指针二维数组复制结果和原来的不同

Question

#include <stdio.h>

void copy_ptr(double(*target)[], double(*source)[], int n);
void show_arr(const double(*target)[], int n);

int main(void)
{
    double source[5][5] =
    {
        {1.1,2.2,3.3,4.4,5.5},
        {1.1,2.2,3.3,4.4,5.5},
        {1.1,2.2,3.3,4.4,5.5},
        {1.1,2.2,3.3,4.4,5.5},
        {1.1,2.2,3.3,4.4,5.5}
    };
    double target[5][5];

    copy_ptr(target, source, 5);
    show_arr(target, 5);

    return 0;
}

void copy_ptr(double(*target)[], double(*source)[], int n)
{
    for (int i = 0; i < n; i++)
    {
        for (int j = 0; j < n; j++)
            (*target + i)[j] = (*source + i)[j];
    }
}

void show_arr(const double(*target)[], int n)
{
    for (int i = 0; i < n; i++)
    {
        for (int j = 0; j < n; j++)
            printf("%g ", (*target + i)[j]);
        putchar('\n');
    }
}

Answer 1

要改成

(*target + i * n)[j] = (*source + i * n)[j];

因为是二维数组，指针要加i * n，不然访问的还是第一层的数组。