First a little recap: A pointer references a location in memory, and obtaining the value at the location a pointer refers to is known as dereferencing the pointer. A null pointer is a variable that makes reference to something that is not initialized. Uninitialized pointer is pointing to some memory location but the pointer value is not assigned.
From my experience in C programming, dereferencing these types of pointers will almost certainly cause a runtime error resulting in a segmentation fault when the compiled program is executed. I'm pretty certain that this applies to Objective C too as the fundamentals are the same. However, my opponent insists that the Objective C language takes care of null and uninitialized pointers by making them point to Nil by default.
To proof that dereferencing null or uninitialized pointers in Objective C will cause runtime errors, I found a simple Objective C sample file online and modified it to compile with gcc in Mac OS X. Attached below are 3 files that are identical except for 1 line of code with the following differences:
- hello.m: with normal initialized pointer
- hello-null.m: with pointer pointing to NULL
- hello-uninit.m: with uninitialized pointer
The screenshot below shows the programs compiled from hello-null.m and hello-uninit.m causing segfaults.
There you have to it: Dereferencing null or uninitialized pointers in Objective C will cause runtime errors resulting in segmentation faults.