Thread: Pointer or array

Never, repeat NEVER, use a pointer for storing data.

A pointer is just a variable that contains an address of something else. Creating a pointer does not create anything for the pointer to point at (the pointee). Writing data through such a pointer yields undefined behaviour .... often, but not always, that means abnormal program termination. It never magically causes memory to be allocated and somehow associated with that pointer.

If you are going to use a pointer, then YOU have to ensure that pointer contains the address of a suitable area of memory. If you do that, then you can use the pointer as if it was an array.

For example;

Code:

int main()
{
     char *prt;
     prt = malloc(100);     /*   prt can now be used as if it was an array of 100 characters */
     printf("Please enter your name: ");
     scanf("%s", prt);        /*  This line will break if the user enters more than 99 characters */
     free(ptr);                  /*  Release allocated memory */
     scanf("%s", prt);        /*  This is now invalid */
return 0;
}

If you use a pointer, you need to make sure it points somewhere.

If you don't initialise your pointer, it's like putting your message in an envelope with random characters where the address should be. Sure it might go somewhere (program works), or the postal service may just throw it in the bin as being meaningless (a segfault).

So these are fairly synonymous:

Code:

char array[100];
scanf("%s",array);
// or
scanf("%s",&array[0]);

char *ptr = malloc( 100 * sizeof(*ptr) );
scanf("%s",ptr);

char array[100];
char *ptr = array;
scanf("%s",ptr);

In each case, the scanf will be able to write up to 100 characters to the memory it has been told about.
It doesn't know (or care) where exactly that memory is (it only has a pointer to it).