autoconf: Null Pointers

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1 13.4 Properties of Null Pointers
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1 Most modern hosts reliably fail when you attempt to dereference a null
1 pointer.
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1    On almost all modern hosts, null pointers use an all-bits-zero
1 internal representation, so you can reliably use `memset' with 0 to set
1 all the pointers in an array to null values.
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1    If `p' is a null pointer to an object type, the C expression `p + 0'
1 always evaluates to `p' on modern hosts, even though the standard says
1 that it has undefined behavior.
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