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The pages on this site contain documentation for very old MS-DOS software, purely for historical purposes. If you're looking for up-to-date documentation, particularly for programming, you should not rely on the information found here, as it will be woefully out of date.

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─────C/C++ Compiler─────────────────────────────────────────────────────────
 
     Syntax:  /Uidentifier
              /u
 
     Option   Description
 
     /U       Turns off definition of specified <identifier>
     /u       Turns off definition of all defined identifiers
 
     The /U (for undefine) option turns off the definition of any
     identifier that is already defined for the preprocessor. The /u
     option turns off every defined identifier. The /U and the /u
     options apply to both predefined names and ones that you define.
 
     Defined identifiers are useful in writing portable programs. For
     instance, they can be used with compiler directives to
     conditionally compile parts of a program, depending on the
     processor and operating system being used.
     See: ◄Predefined Identifiers►
 
     One or more spaces can separate /U and <identifier>. You can specify
     more than one /U option on the same command line.
 
     The maximum number of predefined identifiers is always 30. The /U
     and /u options have no effect on this number.
 
     This example removes the definitions of two predefined identifiers;
     note that the /U option must be given twice to do this:
 
          CL /UMSDOS /UM_I86 WORK.C
 
     See also: #undef
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