Thread: program that segment faults..

Originally Posted by claudiu

A pointer is an address.

int *p = 1; Should segfault immediately because the pointer is not pointing anywhere. (i.e. p has some invalid memory address by default just like a variable has some random value when not initialized).

On the other hand:

int j =1;
int *p = &j;
*p = 2;

Is correct, between p points to the memory location where the value of j resides. (which is a valid memory address)

Okay as per my question 2, doubt is

now u have declared *p =2;
then shouldn't this also mean p=2......Now correct me if i am wrong

my question was why when i define
int *p =1; it takes p =1

and while it not the same other way round *p=2;

Shouldn't it mean that val pointed by p is 2 in both the cases....

Originally Posted by sanddune008

Okay as per my question 2, doubt is

now u have declared *p =2;
then shouldn't this also mean p=2......Now correct me if i am wrong

my question was why when i define
int *p =1; it takes p =1

and while it not the same other way round *p=2;

Shouldn't it mean that val pointed by p is 2 in both the cases....

Sorry I was slightly wrong in my explanation of point 1) -- Lack of sleep

hk_mp5kpdw, explained things better.

Indeed in case 1) int *p = 1; this is setting the address pointed to by p to 1, which is probably an invalid memory location. After you try to dereference the pointer you will get a segfault.

I think your misunderstanding stems from the use of the star(*) operator in two circumstances:

1) int *p; This is telling the compiler here is a pointer p to type int. If you initialize *p on the same line you don't initialize the value contained at the memory location pointed to by p like I wrongly said , but rather the address where p points.

2) A subsequent use of the star(*) operator behind the pointer name refers to the value not the address.

*p = 5; Set the value at address p to 5. However, if p does not point to a valid memory location either dynamically allocated or statically allocated the program will segfault.

I apologize if I confused you even further the previous post.