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7.3  Conditional Compilation

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Often it is desired that a program compile correctly under two or more different circumstances.  In such cases, it is convenient to write a single collection of source and header files, using preprocessor directives to ensure correct compilation for the respective circumstances.  The syntax:

    # define      NAME                 /* no replacement text given */

is used to "define" a name for use with the CONDITIONAL COMPILATION directives:

    # ifdef      NAME
           .
           .
    # else
           .
           .
    # endif

If NAME has been "defined" before the #ifdef directive is encountered, then the



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