How do I print the value at given index in two dimensional array of pointers?

Question

I am trying to print all the values in a two dimensional array. I come from Java and I'm having issues figuring this out in C. How do you access the value at two given indices in C?

void PrintArrayByPointer(int *ptrToArray)
{
    int i,j;

    printf("\nPrint Array By Pointers: \n");
    for(i=0; i<ROWS; i++)
    {
        for(j=0; j<COLS; j++)
        {
            // print the value here
        }
        printf("\n");
    }

    return;
}

It depends on how you store the two dimensional data in a one dimensional array such as ptrToArray. — R Sahu
– R Sahu, Commented Apr 20, 2014 at 3:06
Assuming array data type double and ROWS & COLS are declared global ......... printf("%f",&ptrToArray[i*ROWS + j]) inside j-loop. — DOOM
– DOOM, Commented Apr 20, 2014 at 3:06
@Dukeling: that would be true if ptrToArray were an array of pointers to arrays, but the OP said it's a single 2D array, so because it degrades to a pointer upon passing to a function, you cannot expect ptrToArray[i][j] to work, because there is no way to know the length of each row. — John Zwinck
– John Zwinck, Commented Apr 20, 2014 at 3:07
Can you show where you set up the data you pass to this function? As shown, ptrToArray points to a 1-D array. — M.M
– M.M, Commented Apr 20, 2014 at 5:04

John Zwinck · Accepted Answer · 2014-04-20 03:05:44Z

2

printf("%d ", ptrToArray[i*COLS + j]);

I assume here that your array is stored in row-major order, which is pretty typical in C and C++.

answered Apr 20, 2014 at 3:05

John Zwinck

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Comments

tas · Accepted Answer · 2014-04-20 04:58:47Z

1

It is a better way to change declaration to next one:

void PrintArrayByPointer(int **ptrToArray)

and you can access to array like this:

printf("Value[%d][%d]=%d", i, j, ptrToArray[i][j]);

In your case you should calculate position of your element in array like this:

printf("Value[%d][%d]=%d", i, j, ptrToArray[i*COLS+j]);

answered Apr 20, 2014 at 4:58

tas

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