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| <h3 class="section">A.3 Null Pointer Constant</h3> |
| |
| <p><a name="index-null-pointer-constant-3736"></a> |
| The null pointer constant is guaranteed not to point to any real object. |
| You can assign it to any pointer variable since it has type <code>void |
| *</code>. The preferred way to write a null pointer constant is with |
| <code>NULL</code>. |
| |
| <!-- stddef.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Macro: void * <b>NULL</b><var><a name="index-NULL-3737"></a></var><br> |
| <blockquote><p>This is a null pointer constant. |
| </p></blockquote></div> |
| |
| <p>You can also use <code>0</code> or <code>(void *)0</code> as a null pointer |
| constant, but using <code>NULL</code> is cleaner because it makes the purpose |
| of the constant more evident. |
| |
| <p>If you use the null pointer constant as a function argument, then for |
| complete portability you should make sure that the function has a |
| prototype declaration. Otherwise, if the target machine has two |
| different pointer representations, the compiler won't know which |
| representation to use for that argument. You can avoid the problem by |
| explicitly casting the constant to the proper pointer type, but we |
| recommend instead adding a prototype for the function you are calling. |
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