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1.5.2 Syntax of Conditionals

A conditional in the C preprocessor begins with a conditional directive: `#if', `#ifdef' or `#ifndef'. See section 1.5.4 Conditionals and Macros, for information on `#ifdef' and `#ifndef'; only `#if' is explained here.

1.5.2.1 The `#if' Directive		Basic conditionals using `#if' and `#endif'.
1.5.2.2 The `#else' Directive		Including some text if the condition fails.
1.5.2.3 The `#elif' Directive		Testing several alternative possibilities.