How to: Use #define and #if to Test a Macro

Applies To: Microsoft Dynamics AX 2012 R3, Microsoft Dynamics AX 2012 R2, Microsoft Dynamics AX 2012 Feature Pack, Microsoft Dynamics AX 2012

A macro is a variable known to the precompiler. The variable can have a value that is a sequence of characters, but it is not required to have a value. The #define directive tells the precompiler to create the macro variable, including an optional value. The #if directive tests whether the variable is defined, and optionally, whether it has a specific value.

The value of a macro variable can be written into the X++ code at any location, by giving the name of the macro with the # character added as a prefix.

All precompiler directives and symbols begin with the # character. All of the directives and symbols are handled and removed before the resulting X++ code is given to the X++ compiler.

Defining and Testing a Macro

In the following code sample, a macro named MyMacro is defined. It is not given a value in the #define.MyMacro definition line. Therefore it behaves as if the value is a zero-length sequence of characters.

The #if.MyMacro statement tests whether MyMacro is defined. Because MyMacro is defined, the lines of code before the first #endif are included in the X++ code at the test location.

Near the end of the X++ code there is an #ifnot.MyMacro test. Because MyMacro is defined, that test is false and no lines are written into the X++ code.

After the precompile phase ends for this job, the MyMacro definition goes out of scope and is no longer known to the system.

Code Sample

    static void SimpleDefineIfJob(Args _args)
    {
        str sTest = "Initial value.";
        ;
        #define.MyMacro // MyMacro is now defined.
    
        #if.MyMacro
            sTest = "Yes, MyMacro is defined.";
            info(sTest);
        #endif
    
        // Notice the non-code sentence line causes no X++ compiler error,
        // because the X++ compiler never sees it.
        #ifnot.MyMacro
            The X++ compiler would reject this sentence.
            sTest = "No, MyMacro is not defined.";
            info(sTest);
        #endif
    
    /********** Actual output
    Message (03:46:20 pm)
    Yes, MyMacro is defined.
    **********/
    }

See also

Macros in X++

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