2D阵列-排序| 访问冲突读取位置错误| 在C中

Question

Hey guys I am trying to finish my code but instead of getting values i am getting an error msg .when i am about to enter lien number 54 or 60.

if(*arr[rows*columns]<num) or printf("Number value %d in a two-dimensional size is:%d\n",num,*arr[num]);

This is error msg.

Unhandled exception at 0x013137b2 in LB_12.exe: 0xC0000005: Access violation reading location 0xabababab .

Mission description and the error msg int he next picture. what is wrong? i have to create another array and copy the values if i want the program to print the values?

This is my code

#include <stdio.h>
#include <conio.h>
#include <stdlib.h>
void SortArray(int **arr,int rows,int columns,int num);
void freemalloc ( int **arr,int rows);

void main()
{
    int **arr;
    int i,j,rows,columns,num;
    printf("Please enter the size of 2D array(rows ,cols)");
    scanf("%d %d",&rows , &columns);
    arr=(int **)malloc(rows*sizeof(int *)); // Allocate array of pointers
    if(!arr) // Terms - if there is not enough memory,print error msg and exit the program.
        {
            printf("alloc failed\n");
            return ;
        }
    for(i=0; i<rows; i++)
        arr[i]=(int *)malloc(columns*sizeof(int)); // Allocate memory for each row
    printf("Please fill the 2D array\n");
    for(i=0 ; i<rows ; i++)
        {
            for (j=0 ; j<columns ; j++)
            {
                printf("row:%d columns:%d\n", i,j);
                scanf("%d" , &arr[i][j]);
            }
        }

    printf("Please enter a postive number: ");
    scanf("%d",&num);
    SortArray(arr,rows,columns,num);
    freemalloc(arr,rows);

system("pause");
return;
}
void SortArray(int **arr,int rows,int columns,int num)
{
    int i,j,temp; 
    for(i=0 ; i<rows ; i++ ) // Bubble sort for sorting the 2d array
        {
            for(j=0 ; j<i-1 ; j++ )
            {
                if(arr[i][j]>arr[i][j+1])
                {
                    temp=arr[i][j];
                    arr[i][j]=arr[i][j+1];
                    arr[i][j+1]=temp;
                }
            }
        }
    if(*arr[rows*columns]<num)
        {
            printf("No solution,The maximum value is:%d\n",arr[rows*columns]);
        }
    else
    {
        printf("Number value %d in a two-dimensional size is:%d\n",num,*arr[num]);
    }
}
void freemalloc ( int **arr,int rows)
{
    int i;
    for (i=0 ; i<rows ; i++) // Loop for free the array of pointers
    {
            free(arr[i]); // free each seprate row
    }
    free(arr);
}

Answer 1

My guess is that rows * columns is larger than what you have allocated, meaning you try to dereference a random pointer, leading to undefined behavior and causing the crash.

Also, you will never sort anything, as the outer loop condition is always false (try changing > to < ).

Answer 2

My bet is :

printf("Number value %d in a two-dimensional size is:%d\n",num,*arr[num]);

You're asking for some number and put it in variable num. What makes you think that number num is first number in num-th row?

There might be, and propably are more problems with this code. EDIT:
*arr[num] is evaluated from right to left. [] have higher precedence than * operator.
So it first does arr[num] . and result of that is dereferenced *(arr[num]) . num is treated like a row, so if you don't have enough rows-you got memory violation because you are beyond array