Pointers -C: Doubt

[ShyamCbe]

Hi Buddies

Can u please help me in understanding these codes and their differences.

Code 1

void main()
{
int *p=NULL;
scanf("%d",&p);
printf("\np value: %d",p);
}


Code 2

void main()
{
int *p=NULL;
scanf("%d",p);
printf("\np value: %d",*p);
}

What will be the result of these code and their differences in storage?


Thanks and Regards
Shyam

[Meetee]

Hi Buddies

Can u please help me in understanding these codes and their differences.

Code 1

void main()
{
int *p=NULL;
scanf("%d",&p);
printf("\np value: %d",p);
}


Code 2

void main()
{
int *p=NULL;
scanf("%d",p);
printf("\np value: %d",*p);
}

What will be the result of these code and their differences in storage?


Thanks and Regards
Shyam

Hi Shyam,

First code is correct as in scanf & is preferred and it prints the value given as an output. Second code gives segmentation fault.

Regards

[gpraghuram]

Hi,
Both the code results in segmentation fault.
Since the P is null, u will get this.
Bay the way, have u tried executing this.?
Raghuram

[Meetee]

Hi,
Both the code results in segmentation fault.
Since the P is null, u will get this.
Bay the way, have u tried executing this.?
Raghuram

Hi,

I am running the same code-1 on linux and when I enter value 5 it gives value: 5!!!!!!
It doesn't give segmentation fault!!

Regards

[ilikepython]

Hi,

I am running the same code-1 on linux and when I enter value 5 it gives value: 5!!!!!!
It doesn't give segmentation fault!!

Regards

That might be undefined behaivior. I'm not sure but I think the value the user enters in code 1 is set to the address that the pointer points to, so when you print the pointer you get the same value. I'm not sure about it though.

[Banfa]

Hi,

I am running the same code-1 on linux and when I enter value 5 it gives value: 5!!!!!!
It doesn't give segmentation fault!!

Regards

I suspect that on your C/C++ impementation sizeof(int) == sizeof(int *).

Code 1 erroneously stores the integer value input in the location of a variable of type int * and then treats that variable as it it were an int when it prints it out.

It doesn't give a segmentation fault but is really quite wrong and the code is likely to stop working properly on any system where sizeof(int) != sizeof(int *).