C Tutorial Uninitialized pointers

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Pointer Dereferencing
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Uninitialized Pointers

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When using pointers, there are two entities to keep track of. The pointer and the memory

it is pointing to, sometimes called the "pointee". There are three things which must be

done for a pointer/pointee relationship to work...


(1) The pointer must be declared and allocated


(2) The pointee must be declared and allocated


(3) The pointer (1) must be initialized so that it points to the pointee (2)


The most common pointer related error of all time is the following: Declare and allocate the pointer (step 1). Forget step 2 and/or 3. Start using the pointer as if it has been setup

to point to something. Code with this error frequently compiles fine, but the runtime

results are disastrous. Unfortunately the pointer does not point anywhere good unless (2) and (3) are done, so the run time dereference operations on the pointer with * will misuse and trample memory leading to a random crash at some point.



int* p;


*p = 13;    // NO NO NO p does not point to an int yet

// this just overwrites a random area in memory



Of course your code won't be so trivial, but the bug has the same basic form: declare a

pointer, but forget to set it up to point to a particular pointee.

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