Manual:Zone Manual/General Compiler Information/The VMC pre-processor

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The VMC pre-processor

The VMC Pre-Processor (VMC -p) can be thought of as a powerful search and replace tool used by the compiler before it converts the zone to its binary form. This tool gives you the builder the ability to add comments, create short hand expressions for repeated items, include other files in your zone, and even to do some minor calculations when necessary.

If you have coded in C or c++ before the Pre Processor the VMC uses is no different and you can skip this section.

Commenting your zone

The practice of adding comments to your zone is a good thing to get into so the administrators and other builders can help you with your zone and know what you were trying to do if there are problems. Comments aren't as important when writing the zone as they will be when you start writing your own special DIL functions but it is important to know how comments work and that you can use them if you need to. A comment is a block of text the compiler will never see and is there only for you and who ever reads the file. In order to make it so the compiler will not see the block of text you must surround it by a set of symbols that tell the CPP to strip it out before passing the zone on to the compiler. These symbols are the '/*' and the '*/' symbols or the '//' symbols together in front of a single line.

In order to best explain how comments work we will give you a some what strange example. First we will start by showing you a very basic line you will see time and time again in rooms.

	title "this is a title"

This is a title it will show up in everything from rooms, to objects and even NPCs. Now lets see what a commented line would look like.

	//I am going to make a title now
	title /* I put the keyword
	first*/ "this is a title/*then the title*/

This of course is very ugly but the point is not to be pretty it is to show you both the first way and the second way will look exactly the same to the compiler because all comments are removed before the compiler ever gets it. A better use of a comment in a zone however would be something like this:

	The following ten rooms are the vineyards,
	there are 97 rooms in the zone.

	//Zone first created 1994

You will find comments will make coding large zones much easier because you can add text meant just for the builders eyes.

You will have to decide if you want a multi-line comment or a single line comment and use the '//' or the '/**/' respectively. The rule of thumb is if the comment is longer than 1 line it is easier to put the '/**/' around the comment than to comment each individual line.

Macros and what they can do for you

When making a zone you will find there are things you use more than once. In fact you may find things you want others to use or things you want to use in multiple zones. Its true you could block and copy and stick them everywhere. in fact that is what I did when I first started building. I soon found my zone file was extremely large and hard to upkeep. With a few minor changes and a lot of deleting I used short hand or better known in the world of coding as macros to make my zone readable.

Lets say you had some flags you were going to set in fifty rooms and you knew they would all be the same. You could type the following line 50 times.


With the macros however you could make this much easier by just doing the following at the beginning of your zone.


Then where ever you want the flags you just type DIRTFLOOR. You are probably thinking, yeah big deal I can do that with block and copy. True but there is another benefit to this. Lets say later you wanted to also make these 50 rooms no teleport. All you would have to change is the define like this:


Now when you recompile all 50 rooms are changed and you didn't even have to do a search and replace.

You can also make macros that take arguments. The ability to take arguments is where macros take a leap and a bound out in front of your favorite editor to allow you to do things you can not do easily with search and replace. Lets say you have an exit descr you want to use in 50 swamp rooms because heck everything looks the same in a swamp when you look one direction to the next.

	east to swamp1 descr
	"You see the swamp stretch out for miles";

This could be made into a macro like:

	#define sexit(direction, place) direction to place descr \
	"You see the swamp stretch out for miles.";

Then all you need to use it is:


There is no space between 'SEXIT' and '(' that is important because the CPP sees 'SEXIT(' and 'SEXIT (' as two different things. It is also important to notice all defines must start at the beginning of the line and be either one line long or have a '\' telling the Pre Processor that it should continue with the next line as if it was this line.

You can also combine macros together so you have a set of macros like:

	#define DIRTSECT  movement SECT_INSIDE \

You may have noticed I capitalize all macros. This is not a must but it is suggested so you can easily tell what is a macro and what is not.

Including other files in your zone

Another function of the VMC Pre Processor, '#include', allows you to include other files in your zone file. The VME comes with some basic include files you can use the macros out of and use as examples on how to make your own include files. These files are the composed.h,, vme.h, values.h, base.h, liquid.h, and wmacros.h. Including composed.h will include all the rest of the include files into your zone because it has include statements that use all the others.

You will want to include the files at the beginning of your zone file because all defines you use must be defined before you use them.

Doing minor calculations

You can also do minor calculations in a macro. Lets say you wanted to make it so the higher level an NPC was the heavier he was and the taller he was. This would be simple with a macro.

	#define MLEVEL(lvl) \
	level lvl \
	height lvl+72 \
	weight lvl*9

This macro would increase the height and weight depending on what level you made the NPC pretty simple. There is much more a macro can do for you but the Pre Processor and all its uses go far beyond the scope of this manual. If you are really interested in all the neat things it can do type the following command at the '$' prompt on your Linux box. man cpp The C-Pre Processor is what the VMC Pre Processor is based on and most if not all functions of the CPP work in the VMC.

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