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1.5.2.2 The `#else' Directive

The `#else' directive can be added to a conditional to provide alternative text to be used if the condition is false. This is what it looks like:

#if expression text-if-true #else /* Not expression */ text-if-false #endif /* Not expression */

If expression is nonzero, and thus the text-if-true is active, then `#else' acts like a failing conditional and the text-if-false is ignored. Contrariwise, if the `#if' conditional fails, the text-if-false is considered included.