CODEWITHSUNDEEP
cgenericssyntax
shinzou
shinzou

Reputation: 6222

Passing an element of a generic array to a generic function

We have an array with pointers to generic arrays, and an array of generic functions, we want to apply to each element in array i the function i from func_ptarrs.

typedef struct genarr{
    void * arr;
    int elemsize;
    int numelem;
}GENARR;

typedef void(*funcptr)(void*);

typedef unsigned char byte;

void updateall(GENARR *arrs, funcptr *func_ptarrs, int n){

    int j,i;
    for (i = 0; i < n; i++){
        for (j = 0; j < arrs[i].numelem; j++){

            func_ptarrs[i]((arrs[i].((byte*)(arr + j*arrs[i].elemsize)))); //error: expected member name

            //func_ptarrs[i]((arrs[i].arr)); //no error
        }
    }
}

In the second try it's pointer to the beginning of the array so it's accepted, but I need to be able to send each element of the array to the generic function.

I don't understand how to send the right amount of bytes and move correctly in array all while sending pointers of the elements to the generic functions.

Maybe I should use memcpy?

Upvotes: 0

Views: 647

Answers (1)

Iharob Al Asimi
Iharob Al Asimi

Reputation: 53016

You need this instead,

func_ptarrs[i](((byte*) arrs[i].arr + j * arrs[i].elemsize))

and I think it's pretty obvious why it would work.

You could write accessor macros too, like

#define ARRAY_VALUE(type, x, i (*(type *) ((x).arr + (i) * (x).elemsize))

which you can then use like

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

#define ARRAY_VALUE(type, x, i) (*(type *) ((x).arr + (i) * (x).elemsize))

typedef struct genarr
{
    void * arr;
    int elemsize;
    int numelem;
} GENARR;

int main (void)
{
    GENARR array;
    int    data[10];

    array.arr = data;
    array.elemsize = sizeof(*data);
    array.numelem = sizeof(data) / array.elemsize;

    for (int i = 0 ; i < array.numelem ; ++i)
        ARRAY_VALUE(int, array, i) = i;
    for (int i = 0 ; i < array.numelem ; ++i)
        printf("%d\n", ARRAY_VALUE(int, array, i));

    return 0;
}

Upvotes: 1

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