Tracking null pointer assgn

[Raghavan]

Hi
I have declared this line in my pgm.
char *a=NULL,*b=NULL;
then i used
scanf("%s",a); even i tried gets(a);
its giving null pointer assignment error but pgm works fine and produces correct o/p;

but when i change the pointer to array no error is there
char a[20],b[20]; //no error for this

but i want to use pointers. what can i do

[Dino]

If you declare a pointer, and never associate heap memory with it, then the pointer is not initialized.

When you declare and use an array, the memory is allocated for you in the program stack.

So, you need to malloc() some storage.

Todd

[matsp]

You need to give your pointers some memory, for example with malloc().

Given that it doesn't crash when accessing a NULL pointer hints to me that you are running in DOS-mode - for example using Turbo C - try finding a compiler that at least produces 32-bit code.

--
Mats

[Elysia]

And don't use gets, use fgets.
Nor should you use scanf("%s", a). Read my signature on how to do it properly.

[Salem]

> its giving null pointer assignment error but pgm works fine and produces correct o/p;
You're using DOS aren't you, which has no memory protection.

Always remember, "works" != "bug free". You can do all sorts of dumb stuff, and the program can still manage to produce the result you expect.

Try it on say Linux, and you're looking down the barrel of a segmentation fault.