C251 User's Guide

#elif

The #elif directive tests an expression and if the result is true (non-zero) allows the compiler to process subsequent text (until the next #else, #elif, or #endif directive). If the result is false (zero), subsequent text is not processed by the compiler. The #elif directive may be used only after a #if directive has been specified.

#if expression
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#elif expression
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#elif expression
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#else
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#endif