How to understand this code?

Question

#include <iostream.h>

void increase (void* data, int type) {
switch (type) {
case sizeof(char) : (*((char*)data))++; break;
case sizeof(short): (*((short*)data))++; break;
case sizeof(long) : (*((long*)data))++; break;
}
}

int main () {
char a = 5;
short b = 9;
long c = 12;
increase (&a,sizeof(a));
increase (&b,sizeof(b));
increase (&c,sizeof(c));
cout << (int) a << ", " << b << ", " << c;
return 0;
}

Answer 1

A void pointer is a special pointer that can point and be casted to any generic type, as it has no type at all in general.

But this makes it impossible for such a pointer to be dereferenced directly, or to perform arithmetic operations like increment and decrement.

Thus, such a pointer is used by casting it to a different type and then dereferencing it.

In your case, you pass a type of pointer and its size to the function. The function then stores your argument in a void pointer as casts it accordingly as per the switch cases for the size.

The line ((char*)data), will cast the void pointer to a char pointer if the size of the pointer is received as 1.

The rest of the part dereferences he casted pointer and increments the value.