为什么这个矩阵点积程序在某些情况下会在最后一列打印地址？

Question

我编写了这个程序来计算两个矩阵的点积。它在几种情况下工作正常，但在我测试时我注意到它在最后一列中打印了似乎是地址的内容，我无法弄清楚为什么。具体针对以下输入：3 2 3 1 2 1 1 1 2 1 2 3 3 2 1

我正在使用 CodeBlocks 编译和运行代码。另外，我对C比较陌生。

#include <stdio.h>
#include <stdlib.h>

//Method to allocate memory for a 2D array
int** allocateMatrix(int rows, int columns)
{
    //Declaration of variables
    int **matrix, i;

    //Allocate memory to store 'rows' many pointers to integers
    matrix = malloc(rows*sizeof(int*));

    //For-loop to allocate memory to store 'columns' many integers, and initialize them to zero
    for (i=0; i<rows; i++)
    {
        matrix[i] = calloc(0,columns*sizeof(int));
    }

    return matrix;
}

int main()
{
    //Declaration of variables
    int n, m, p; //used as matrix dimensions
    int i, j, k; //used in for-loops

    //Read input
    do
    {
        //printf("Enter value of rows for first matrix (greater than 0):\n");
        scanf("%d", &n);
    }while(n<0);

    do
    {
        //printf("Enter value of columns for first and rows for second matrix (greater than 0):\n");
        scanf("%d", &m);
    }while(m<0);

    do
    {
        //printf("Enter value of columns for second matrix (greater than 0):\n");
        scanf("%d", &p);
    }while(p<0);

    //Create three matrices, by calling 'allocateMatrix' function
    int** matrix1 = allocateMatrix(n,m);
    int** matrix2 = allocateMatrix(m,p);
    int** matrix3 = allocateMatrix(n,p);

    //Two for-loops to store values in 'matrix1'
    //For-loop to go through rows
    for (i=0; i<n; i++)
    {
        //For-loop to go through columns
        for (j=0; j<m; j++)
        {
            //Read input
            scanf("%d", &matrix1[i][j]);
        }
    }

    //Two for-loops to store values in 'matrix2'
    //For-loop to go through rows
    for (i=0; i<m; i++)
    {
        //For-loop to go through columns
        for (j=0; j<p; j++)
        {
            //Read input
            scanf("%d", &matrix2[i][j]);
        }
    }

    //THREE for-loops to multiply values in 'matrix1' and 'matrix2' and store results in 'matrix3'
    //For-loop to go through rows of 'matrix3' and 'matrix1'
    for (i=0; i<n; i++)
    {
        //For-loop to go through columns of 'matrix3' and 'matrix2'
        for (j=0; j<p; j++)
        {
            //For-loop to go through columns of 'matrix1' and rows of 'matrix2'
            for(k=0; k<m; k++)
            {
                //Read input
                matrix3[i][j] = matrix3[i][j] + (matrix1[i][k] * matrix2[k][j]);
            }
        }
    }

    //Print the resulting matrix
    //Two for-loops to print values in 'matrix3'
    //For-loop to go through rows
    for (i=0; i<n; i++)
    {
        //For-loop to go through columns
        for (j=0; j<p; j++)
        {
            if (j==p-1) //for correct format
            {
                printf("%d", matrix3[i][j]);
            }
            else
            {
                printf("%d ", matrix3[i][j]);
            }
        }
        //Change line
        printf("\n");
    }

    //Free the memory up!!!!
    free(matrix1);
    free(matrix2);
    free(matrix3);

    return 0;
}

Answer 1

你没有在这里分配任何内存:

matrix[i] = calloc(0,columns*sizeof(int));

calloc 的第一个参数设置要分配的元素数。在这种情况下，它应该是 columns

matrix[i] = calloc(columns,sizeof(int));

同时确保您验证了您的 scanf 输入。

为什么这个矩阵点积程序在某些情况下会在最后一列打印地址？

Why does this matrix dot product program print addresses in the last column in some cases?

c

matrix

printf

dot-product