Thread: #define question

An interpreter is basically an application that parses some text and evaluates it and does something with it.
Javascript and PHP are, for example, interpreted languages, since a parser parses the code and translates it into executable code.

You could just allow your "workers" to write pseudo code or some criterias or whatever and then parse and do something with this. This is an interpreter.

I think dudeomandude has the right idea. Build a simple GUI that you can enter some criteria in, and let that run.

But you can make it more complex by building a parser for a simple (or complex) language.

Using #define to create a criteria in a header file that is later compiled into an application is absolutely the wrong way to solve the problem. It is going to be error prone for one thing. Imagine what happens if someone does a typo in the macro definition, and then the compile goes wrong - are they going to understand the error message of this??

Code:

#define Criteria Number == 5;

--
Mats

That sounds very interesting actually. I have to ask anyway.
If I take this just as an example:

If I have this:

Code:

int Number1 = 5;
int Number2 = 6;

And then I will write this text below in a textBox:
Where the C++ code will look like this: if (parsed text in textBox) {Action;}

if

Code:

(Number1 == 5 && Number2 == 6)   //This is written inside a textBox

{
Action;
}

So I might wonder if it is possible to use a textBox and from there parse out every word and convert the 5 and 6 to ints etc.

Yes, that can be done.

What may be a little bit difficult is to translate "Number1" so that it gets compared with the variable Number1 in your code. But it's all doable.

--
Mats

What technique should I use to do this. I dont really know what the first step could be to do.

Because the "criteria" written in the textBox has to be replaced with executable code.
For me it sounds like I have to have somekind of "list with emty spaces" where I put the parsed code in something like this below. I dont know if I am thinking right here and then let the criteria always go through this recognicible list.

I just dont know where the parsed code will be put and recogniced within the C++ code otherwise.

Code:

Number1
== 
5
&&
Number2
== 
6

If you want an easy parser, the easiest way would be to require an exact layout. Say for example, you want to parse this:
if (Number1 == 1)

First you would extract all characters until the whitespace (between "if" and "("), lookup a function through a map and call it. This is the "if" parser function.
The if parser function would then potentially check for a "(", otherwise scream parse error.
Then it would extract everything until whitespace (between "Number1" and "=="). It may interpret this as a variable.
It then parses until a new whitespace and, in this example, finds "==". Looks up via a map and calls "equality function". Equality function reads the number until ")" (or potentially up until a newline), and then checks if a this variable equals this value and return true or false.
The "if function" return true if the "action" inside the if should be executed or not and the main parser behaves accordingly.

This is an example of how to write a parser, but I'm too lazy to write any pseudo code right now, sorry.

No problem! Thanks, this is anyway letting me know the picture of how it could be done. I will check up how maps works as I dont know that and begin one step at a time.
So it is kind of communication beween parsed values etc to be recogniced in the map.

Using a method like this, will it slow down the running of the code for example if you read from .txt files and this criteria is refering
to values red in the files ?

The maps makes it easier and, probably faster, as well. Otherwise you could continue parsing and make functions or big if nests, but that's nasty. And a parser can be quite slow.

Originally Posted by Coding

Using a method like this, will it slow down the running of the code for example if you read from .txt files and this criteria is refering
to values red in the files ?

Reading from files is always a little slower, but it won't make much of a performance impact for this, I would think.

On a side note, C++ offers an implementation of a map in std::map.

I tried to write std::map in my code but couldn´t find this member.
Perheps I have to include something.

Include <map>
Also be aware that you're treading into the Managed/Native boundary again. std::map is for native and not managed, but if you do this on C++ .NET, you'll find yourself with String^ a lot of which won't work at all with std::map. I'm sure there is a managed map, but I don't know its name.

Is it not located under std? If it isn't, then it's not C++'s map, so it might well be a managed map.