When a Script or Template is executed, a special preprocessor stage is run before the main compilation of the file begins. In the preprocessor stage, the software finds any preprocessor directives (e.g. #include, #ifdef, #define, etc.) and uses them to modify the text of the original source code. Each preprocessor directive must start with a '#' character and the '#' character must be the first non-whitespace character on a line.

Defines

Special preprocessor constants can be defined using the syntax '#define <constant_name> [ <text_value> ]'. For example:

    #define PI 3.14159265

Note that a semi-colon is not required after the statement. When any occurrence of the defined constant name is encountered in the rest of the source code (except inside of a string), it will be textually replaced with the defined value of the constant. For example:

    Printf( "ToRadians=%lf\n", 90.0 * (PI/180.0) );

When defining a constant, a value is not required after the constant name in which case a constant is still defined but it will have an empty value. The constant value can be any text string and multi-line values can be defined by placing a '\' character as the last character of a value line. For example:

    #define CHECK_VALUE if( value > 5) { \
        Printf( "Invalid value %d\n", value ); \
        Exit(-1); }
    
    int value = 4;
    CHECK_VALUE;
    value = 10;
    CHECK_VALUE;

The constant '_010EDITOR' is always defined when running 010 Editor. Any constants that are defined can be undefined later using the syntax '#undef <constant_name>'. Note that some preprocessors support macros with #define statements but this is not currently supported in 010 Editor.

Conditional Compilation

The preprocessor directives #ifdef and #ifndef can be used to compile or ignore whole sections of source code depending on if certain constants were defined with the #define directive above. The syntax for these commands is:

    #ifdef | #ifndef <constant_name>
       (...)
    [ #else ]
       (...)
    #endif

A common usage of this syntax is to place code such as:

    #ifndef CONSTANTS_H
    #define CONSTANTS_H

at the beginning of a header file (e.g. constants.h) and then an '#endif' statement at the end of the header file. Then, if this header file is included twice into the source code with #include (see below), the code inside the header file will only be compiled once (the second time the file is included the constant CONSTANTS_H is already defined so the #ifndef statement skips the rest of the code). Note that multiple #ifdef or #ifndef statements can be nested inside of each other, but make sure the #endif statements properly line up with the #ifdef/#ifndef statements.

Warnings and Errors

The preprocessor directive #warning can be used to output a message to the Output tab of the Output Window during compilation with the syntax '#warning "<message>"'. For example:

    #ifdef NUMBITS
        value = value + NUMBITS;
    #else
    #warning "NUMBITS not defined!"
    #endif

The #error directive is similar to the #warning directive except compilation will stop once an #error directive is reached. For example:

    #ifndef CURRENT_OS
    #error  "CURRENT_OS must be defined. Compilation stopped."
    #endif

Includes

The #include directive is supported to insert additional text files into the current file. This directive is discussed in the separate Includes help topic.