how to dereference a void pointer

A void pointer can hold address of any type

if the pointer know the address of another variable, then we can change the value store in that address by pointer dereference

In a code ptr hold the address of variable a

how to modify value of a ?

Code:

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#include<stdio.h>

int main()
{
    int a = 10;


    void *ptr = &a;


    printf("%d", *(int *)ptr);
       
        *ptr = 12;
       
        printf("%d", *(int *)ptr);


    return 0;
}

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error invalid use of void expression

You need to case the "vold *" to a "something *" so the compiler knows what sort of data you are accessing (e.g. char, short, int, long, float double, a structure...)

Code:

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*((int *)ptr) = 12;

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