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Passing pointer problem

Started by DaWookie May 30, 2002 at 9:14 PM 3 replies 250+ views

Original Post

May 30, 2002 at 9:14 PM

//Exercise in futility// #include <stdio.h> #define MAX 3 //Variables// int array1[MAX]; int array2[MAX]; int counter = 0; int *ptr; //Prototypes// int *addarray(int *ptr1, int *ptr2); main() { for(counter = 0; counter < MAX; counter++) { printf("\nEnter a value for array1[%d]", (counter+1)); scanf("%d", &array1[counter]); printf("\nEnter a value for array2[%d]", (counter+1)); scanf("%d", &array2[counter]); } addarray(array1,array2); for(counter = 0; counter < MAX; counter++) { printf("\nArray1[%d] + Array2[%d] = %d", counter, counter, *ptr ); ptr++; } return 0; } int *addarray(int *ptr1, int *ptr2) { int total = 0; int holdarray[MAX]; for(counter = 0; counter < MAX; counter++) { total = *ptr1 + *ptr2; ptr1++; ptr2++; holdarray[counter] = total; total = 0; } for(counter = 0; counter < MAX; counter++) { printf("\n Holdarray[%d] = %d", counter, holdarray[counter]); } ptr = holdarray; return ptr; } when compiled and ran...i get a valid total in holdarrays printf portion, but the pointer sent back to main which holds the starting address of holdarray when incremented is not working past its first intial use. I have verified that ptr is incrementing correctly, which almost makes me think that holdarray''s mem is being released be4 i access it with my pointer? why if i can get the first value from pointer correct can i not increment by ptr++ and get the next value from holdarray like i should? i appreciate any help..i am just starting to try to grasp pointers in c

aNonamuss

May 30, 2002 at 9:29 PM

In function addarray you declare holdarray[MAX]. But once function addarray returns control to main, holdarray goes out of scope. Therefore ptr is pointing to memory that has been released and could possibly contain garbage data.

Perhaps declare holdarray as global, or you could declare it as static in function addarray:


int *addarray(int *ptr1, int *ptr2)
{
    static int holdArray[MAX];    
             |
             |
}

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[edited by - aNonamuss on May 30, 2002 10:32:33 PM]

DaWookie

Author

DaWookie

May 30, 2002 at 9:41 PM

thanks for the help

i cant believe i missed that, i thought i had declared holdarray as globlal on a previous build and that it hadnt worked, but i think i may have had it declared in two places or some other problem...
going global fixed it, i am going to take a closer look at the static solution
thanks again

aNonamuss

May 30, 2002 at 9:44 PM

You could even do away with a the globals and optimize your code a bit by doing the following. Just a thought:

      
//Exercise in futility//

#include <stdio.h>

#define MAX 3


//Prototypes//

int *addarray(int *ptr1, int *ptr2);

main()
{
    int counter;
    int array1[MAX];
    int array2[MAX];

    for(counter = 0; counter < MAX; counter++)
    {
        printf("\nEnter a value for array1[%d]", (counter+1));
        scanf("%d", &array1[counter]);

        printf("\nEnter a value for array2[%d]", (counter+1));
        scanf("%d", &array2[counter]);
    }

    int *ptr = addarray(array1,array2);

    for(counter = 0; counter < MAX; counter++)
    {
        printf("\nArray1[%d] + Array2[%d] = %d", counter, counter, *ptr );
        ptr++;
    }

    return 0;
}


int *addarray(int *ptr1, int *ptr2)
{
    int counter;
    static int holdarray[MAX];

    for(counter = 0; counter < MAX; counter++)
    {
        holdarray[counter] = *ptr1 + *ptr2;
        ptr1++;
        ptr2++;
        printf("\n Holdarray[%d] = %d", counter, holdarray[counter]);

    }

    return holdarray;
}

[edited by - aNonamuss on May 30, 2002 10:50:01 PM]

DaWookie

Author

DaWookie

May 30, 2002 at 10:06 PM

interesting...

I was wondering about passing holdarray back directly without going vi a pointer, but i guess thats impossible. Instead i see u assigned holdarray[0]''s address to *ptr.
Thanks for the cleaning the code a little.

I was trying to pass holdarray back directly for awhile

but i guess return doesnt like to pass along more than one value...go figure.

But, i see that u can still pass its address to another pointer and reference from there.

thanks for all the info..i actually learned something

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