Question

While reading tutorials regarding pointers, i faced a code like this

const int *p;

and

int const *p;

and

int *const p;

Whats the main difference in them?

While i assigned any integer value’s address,like

int b=100;
b=&p;

i am getting errors. Whats the point in this? Can anybody explain it with example?

Answer 1

Most of the time, simply read it from right to left.

int const *p;

“p is a pointer to a const int“.

int *const p;

“p is a const pointer to an int“.

The exception is when const is the lefmost keyword:

const int *p;

Then it’s the same as:

int const *p;

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If the pointer is const, then you can’t modify its address, but you can change the value pointed by it. If the pointed to value is const (an int in your case), then you can’t modify what’s pointed to by the pointer (but you can make it point to something else).

As an unrelated thing, this fails to compile:

int b=100;
b=&p;

Because you’re assigning the address of the pointer veriable (a int **) to b. It’s an illegal conversion. You could force it with a cast, but I don’t think that’s what you want.