在C++中调用指针函数

Question

我用C++编写了一段代码.我从搜索引擎结果中获取了第一部分.

1)使用函数定义函数的含义是什么double **filter_2d？我们可以使用指针定义函数吗？

2)我对以下行感到困惑:

double **filt_out = filter_2d(A, 3, 3, B, 2, 1);

它工作不正常,我不明白为什么.

#include <iostream>
#include <stddef.h>
#include <cmath>
#include <fftw3.h>
using namespace std;

void filter_2d(double** image, int width_image, int height_image, double** kernel, int width_kernel, int height_kernel, double *** OutImg)
{
    double **output = *OutImg;
    int i, j, p, q;

    //this is the case of 'full' option selected in matlab
    //double **output = (double **)malloc(sizeof(double *)*(width_image + width_kernel - 1));
    for (i = 0; i<width_image + width_kernel - 1; i++)
    {
        output[i] = (double *)malloc(sizeof(double)*(height_image + height_kernel - 1));
    }

    //for each point in the output
    for (i = 0; i<width_image + width_kernel - 1; i++)
    {
        for (j = 0; j<height_image + height_kernel - 1; j++)
        {
            output[i][j] = 0;
            //kernel(p,q)*image(i-p, j-q) 
            for (p = 0; p<width_kernel; p++)
            {
                //avoid unnecessary comparisons
                if (i - p < 0)
                {
                    break;
                }
                else if (i - p < width_image)
                {
                    for (q = 0; q<height_kernel; q++)
                    {
                        //idem as above
                        if (j - q < 0)
                        {
                            break;
                        }
                        else if (j - q < width_image)
                        {
                            output[i][j] += kernel[p][q] * image[i - p][j - q];
                        }
                    }
                }
            }
        }
    }
}

int main()
{
    double ** OutImage = 0;
    OutImage = (double **)malloc(sizeof(double *)*(3 * 3));

    double A[3][3] = { { 1, 2, 3 },
    { 4, 5, 6 },
    { 7, 8, 9 } };
    double *A_ptr[9];
    for (int i = 0; i < 10; i++)
    {
        A_ptr[i] = A[i];
    }
    double B[1][2] = { 1, 2 };
    double *B_ptr[2];
    for (int i = 0; i < 2; i++)
    {
        B_ptr[i] = B[i];
    }
    //Error in the below line
    filter_2d(A_ptr, 3, 3, B_ptr, 2, 1, &OutImage);  //unable to understand
    for (int i = 0; i < 5; i++)
    {
        for (int j = 0; j < 4; j++)
            cout << *OutImage << endl;
    }
    system("PAUSE");
    return 0;
}

Answer 1

指针声明
一般格式:

data_type *pointer_name;

一个指针声明,如,

int *numberPtr; 

将numberPtr声明为指向整数变量的变量.它的内容是一个内存地址.

*表示声明的变量是指针变量而不是普通变量.

请考虑以下声明:

int *numberPtr, number = 20;  

在这种情况下,保留了两个存储器地址,与名称numberPtr和number相关联.

变量号中的值是整数类型,变量numberPtr中的值是另一个内存位置的地址.

例

// create a 2D array dynamically
int rows, columns, i, j;
int **matrix;
cin >> rows >> columns;
matrix = new int*[rows];
for(i=0; i<rows; i++)
   matrix[i] = new int[columns];