Question

#include <iostream>
#define n 255

using namespace std;


int main()
{
int i=n;
int *ptr=&i;
int const *ptr_1=&i;
const int *ptr_2=&i;
const int * const ptr_3=&i;
}

Why does this Code Compile in Visual C++, Dev C++ and G++?
Link to – Ideone –

Answer 1

It does compile, because all those pointers ether don’t change const-qualification of the variable access or enforce the qualification, but none of them tries to loosen the qualification.

For example:

const int var;
int* address = &var; //illegal - tries to remove const

would try to get non-const access to a const variable and that’s illegal, but

int var;
const int* address = &var; //legal - only adds const

tries to get const access to a non-const variable and that’s legal since a non-const variable does allow const-only access.