#IFDEF | #IFNDEF ... #ENDIF Preprocessor Directive

Conditionally includes a set of commands at compile time if a compile-time constant is defined.


#IFDEF | #IFNDEF ConstantName 
      Commands
[#ELSE 
      Commands]
#ENDIF

#IFDEF

Specifies that a set of commands is included at compile time when the ConstantName is defined.

The following items describe how a set of commands is included at compile time when you include #IFDEF:

  • If ConstantName is defined, the set of commands following #IFDEF and preceding #ELSE or #ENDIF (whichever occurs first) is included at compile time.

  • If ConstantName is not defined and #ELSE is included, the set of commands following #ELSE and preceding #ENDIF is included at compile time.

  • If ConstantName is not defined and #ELSE is not included, no commands within the #IFDEF ... #ENDIF structure are included at compile time.

#IFNDEF

Specifies that a set of commands is included at compile time when the ConstantName is not defined.

The following items describe how a set of commands is included at compile time when you include #IFNDEF:

  • If ConstantName is not defined, the set of commands following #IFNDEF and preceding #ELSE or #ENDIF (whichever occurs first) is included at compile time.

  • If ConstantName is defined and #ELSE is included, the set of commands following #ELSE and preceding #ENDIF is included at compile time.

  • If ConstantName is defined and #ELSE is not included, no commands within the #IFNDEF ... #ENDIF structure are included at compile time.

ConstantName

Specifies the compile-time constant whose existence determines whether a set of commands is included at compile time. Compile-time constants are defined with #DEFINE.

Commands

Specifies the set of commands that is included at compile time.

You can nest an #IFDEF | #IFNDEF ... #ENDIF structure within another #IFDEF | #IFNDEF ... #ENDIF structure.

Comments can be placed on the same line after #IFDEF, #IFNDEF, #ELSE, and #ENDIF. These comments are ignored during compilation and program execution.

The following example creates a compile-time constant named MYDEFINE. #IFDEF ... #ENDIF displays a message if the compile-time constant has been defined.

#DEFINE MYDEFINE 1

#IFDEF MYDEFINE   
   WAIT WINDOW "MYDEFINE exists"
#ELSE
   WAIT WINDOW "MYDEFINE does not exist"
#ENDIF

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