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Another use of conditional compilation is to avoid reinclusion of header files which are themselves #included into other headers.  (TC provides a simpler method to accomplish this.*)  For a header file named 'filename.h', a common approach is to begin the file with:

    # ifndef     filename_h             /* like #ifdef, but means "if not defined" */
    # define    filename_h

and end the file with:

    # endif

Also, note that it is legal to nest #ifdef/#endif conditions.

Certain names are defined automatically by the system in use.  For example, the name THINK_C is defined whenever the TC compiler is in use.  The following section demonstrates how to allow TC programs to compile equally under C++.

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54516

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TC feature to prevent header reinclusion

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TC feature to prevent header reinclusion - p177