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This recommendation is derived from and considers the implications of the following common conventions:
(1) Function failures are can typically be indicated by one of the following return values: 0, -1, a non-negative zero number.
(2) Functions return 0 if false, but only non-zero if true.
(3) Comparison functions (such as the standard library function strcmp()) return 0 if the arguments are equal and non-zero otherwise.
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