Pass struct array to function

Question

I want to assign a1 into ana[0], ana1 only inside the storeDataHere function.

Inside saveData function, just need to pass each data_array[0] to storeDataHere function.

#include <stdio.h>
#include <string.h>
struct Analysis{
    int a;
    int b[10];
};

struct Analysis ana[2];

void storeDataHere(void* res)
{
    // initialize a1;
    struct Analysis a1;
    a1.a = 1;
    memset(a1.b, 0, 10*sizeof(int));

    for(int i=0; i<10; i++)
        a1.b[i] = 1;


    // store a1 into ana[0], ana[1];
    struct Analysis temp = res;
    temp = a1;

}

void saveData(void* data, size_t size)
{

    struct Analysis *data_array = data;
    // pass two struct elements to storeDataHere;
    storeDataHere((void*)data_array[0]);
    storeDataHere((void*)data_array[1]);
}



int main()
{
    // pass struct array ana to saveData
    saveData( (void*)ana, sizeof(ana[0]));

    for(int i=0; i<2; i++)
    {
        printf("\n%d\n", ana[i].a);
        for(int j=0; j<10; j++)
            printf("%d", ana[i].b[j]);
    }

    return 0;
}

Here is the output with errors:

How to solve this if I keep this structure of function? (Not to change the function param)

you probably need to change this struct Analysis temp = res; to this struct Analysis* temp = res; — Anatoly Strashkevich
– Anatoly Strashkevich, Commented Sep 10, 2016 at 5:31
Another of your classmates has also inquired about this assignment: stackoverflow.com/questions/39419832/…. I suggest you read his question and its answer, as they may be helpful. — John Bollinger
– John Bollinger, Commented Sep 10, 2016 at 5:35
also, instead of storeDataHere((void*)data_array[1]);, try to use storeDataHere((void*)(data_array + sizeof(struct Analysis)*offset); — Anatoly Strashkevich
– Anatoly Strashkevich, Commented Sep 10, 2016 at 5:35
Also, I think that converting your void * to a struct Analysis * in function saveData() is likely missing the point of the exercise. One would declare the function parameter as a struct Analysis * in the first place if the function was meant to be specific to that data type. — John Bollinger
– John Bollinger, Commented Sep 10, 2016 at 5:41
@JohnBollinger: Interesting: you've found a third person working on this exercise — there's also stackoverflow.com/questions/39404854/…? by another user, mdadurian, with the same struct Analysis and passing the data around via void *. I used search term '[c] struct analysis is:q' and ordered by newest. I'd come across Patrick and mdadurian (and this homework problem) before — and not Jam. — Jonathan Leffler
– Jonathan Leffler, Commented Sep 10, 2016 at 6:19

Khiem Tran · Accepted Answer · 2016-09-10 05:47:02Z

2

See answer here:

https://repl.it/D2Cd

// use struct Analysis* instead of void*
//
void storeDataHere(struct Analysis* res)
{
    int i;
    // initialize a1;
    struct Analysis a1;

    a1.a = 1;
    // memset(a1.b, 0, 10*sizeof(int)); no need to memset cause you set later

    for (i = 0; i < 10; i++) 
    {
        a1.b[i] = 1;
    }

    // store a1 into ana[0], ana[1];
    *res = a1; // assign value of pointer res to a1 
}

// pass array struct to function
void saveData(struct Analysis data[])
{
    struct Analysis *data_array = data;
    // pass two struct elements to storeDataHere;
    storeDataHere(&data_array[0]);
    storeDataHere(&data_array[1]); // pass pointer of each element to StoreDataHere
}

See the link for more details. Happy coding!!

answered Sep 10, 2016 at 5:47

Khiem Tran

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Comments

Saurav Sahu · Accepted Answer · 2016-09-10 05:41:21Z

1

Change (you need to cast void pointer and then dereference):

struct Analysis temp = res;

to

struct Analysis temp = *((struct Analysis *)res);

Another correction (cast and pass the correct type):

storeDataHere((void*)data_array);

answered Sep 10, 2016 at 5:41

Saurav Sahu

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Comments

masoud · Accepted Answer · 2016-09-10 05:43:46Z

1

You're trying to assign a pointer to an object, that's impossible, to have a copy you should:

// Copy values
struct Analysis temp = *((struct Analysis*)res);

// or
// Copy pointer
struct Analysis *temp = res;

Next problem is, passing elements of data_array such as data_array[0] to the function (according to your code), you must pass whole structure:

storeDataHere((void*)data_array);

edited Sep 10, 2016 at 5:43

answered Sep 10, 2016 at 5:35

masoud

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