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What is NULL and how is it defined?
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What is NULL and how is it defined?
As a matter of style, many programmers prefer not to have unadorned 0's scattered through their programs, some representing numbers and some representing pointers. Therefore, the preprocessor macro NULL is defined (by several headers, including and ) as a null pointer constant, typically 0 or ((void *)0) A programmer who wishes to make explicit the distinction between 0 the integer and 0 the null pointer constant can then use NULL whenever a null pointer is required.
Using NULL is a stylistic convention only; the preprocessor turns NULL back into 0 which is then recognized by the compiler, in pointer contexts, as before. In particular, a cast may still be necessary before NULL (as before 0) in a function call argument.
NULL should be used only as a pointer constant
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