#define question

I will try to explain and see how much I understand.
in void Help() it start to find the first space in the string wich is after "if" as we know, wich then is strToParse.find(" ");
After this we then check the indexes. As the string always start on 0, the if will have
index: substr(0, 2) and this is now our strKeyword, wich should be "if"

Later we write:

Code:

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if ( ParseMap.find( strKeyword.c_str() )    // wich puts the found "if" to c_str()

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As the keyword for ParseMap is "if" this could evaluate to true if these matches ?
What I then dont understand is what happens here:

Code:

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->second( strToParse.substr(index + 1) ) )

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Am I thinking right.

No, not quite.
We search for the keyword in the map. The member function find returns an iterator to the element in the map.
To access the actual value stored in the map, we must dereference the iterator and access the member "second" which contains the actual value and type stored in the map. In our map, we store function pointers, so we can call these.
So in effect, the if checks the return from the function.

Also remember that the pointers in the map points to a function that takes a std::string as argument, so we need to pass that, as well. So what we do is pass the string after the space - the part of the string the "If function" should parse.

> we must dereference the iterator and access the member "second" which contains the actual value and type stored in the map.

I think I get the logic more now. I have to ask about this part. Is the member "second" in this case: &ParseIf that point to the Acutal value: bool ParseIf(const etc...) below that contains a whole function and rules about if ?
If it does, where in this function does it tell that the now found "if" will work as if.

Yes, this is the essence of how it works.
As for how... well, it's a map. We look up "if" and find the value stored in the map for "if" which in this case is the address of a function. The function for parsing if.
Later you can add other values to the map. It will automatically find the correct function and call it.

Okay I think I understand much more now. I will try to sum up some wonderings to cover.

In the 3 functions we have:

Code:

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if ( ParseMap.find
return ParseMap2.find
return (VariablesMap.find

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I am not really sure here. In void Help() we have the acutal string, strToParse and in this function we have ParseMap.find.
Does this function only looking for "if" and ParseMap2 only for "==" and VariablesMap only for "Number1" ?

Because what I like to understand is that the "if (Number1 == 1)" must somewhere be readed from left to right while parsing out everything with " " and for each "thing" that is found will be associated automatically with the pointers.
Have I missed if this is happening somewhere. Because something must be readed from left to right to be understandable ?

My second question is:
What happens here. Does Help() represents: if (Number1 == 1). I might wonder where the acutal statement takes place and can evaluate to true or false.

Code:

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int main()
{
        Help();
        return 0;

}

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You can delete your posts, you know, if you feel that you didn't need to reply or ask. I do it often.

Yes I saw that I could do that now...thanks..

Quote:

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Originally Posted by Coding

I am not really sure here. In void Help() we have the acutal string, strToParse and in this function we have ParseMap.find.
Does this function only looking for "if"

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The first function looks for kind of line we have here. Is it an if, or something else? Its job is to interpret what kind of line it is and direct the parsing to the appropriate function that can continue to parse the line.
The reason for this is that each line can look differently. Therefore, by identifying what kind of line it is, it can continue to parse the line and extract the relevant information. But this extraction process is continued elsewhere.

The ParseMap contains the keywords that identifies what kind of line it is.

Quote:

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...and ParseMap2 only for "=="...

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ParseMap2 is necessary for functions that takes two arguments. This is why ParseIf searches the second map for the operation function to call.

Quote:

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...and VariablesMap only for "Number1" ?

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The VariablesMap is an example of a map that holds variables in your program that you've read from somewhere. It maps strings to longs.

Quote:

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Because what I like to understand is that the "if (Number1 == 1)" must somewhere be readed from left to right while parsing out everything with " " and for each "thing" that is found will be associated automatically with the pointers.
Have I missed if this is happening somewhere. Because something must be readed from left to right to be understandable ?

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But it is.
Read up until first space:
if (Number1 == 1)
Finds the string in red.
Looks it up in the map. Finds a function for the keyword. Calls function with the rest of the string to parse (colored green).
ParseIf knows that we're parsing an if line here so it knows that the first thing to find will be a variable, so it searches for a space. It also does a check to see if the first character in the string is a "(". This is to make sure the syntax is correct only.
ParseIf receives this string:
(Number1 == 1)
It searches for the space between the operation and the variable and extracts it (save for the "("), so it extracts the red part.
Now it has the variable. Now it must know what kind of operation is to be done. What to check.
So it searches for the next space between the operation and the number to check against (marked in blue).
Once it extracts that, it searches in the map for the appropriate function to call for this operation. It passes along the variable name (the one in red) and the rest of the string to parse (marked with green).

And last, OperationEqual knows that it must compare the variable Number1 against a number.
The function has the following string to parse:
1)
So it searches for the "(" and extracts the text before that (marked in red).
It then converts that to a number and looks up the current value for the variable received through the argument (Number1 in this case) in the map and compares it to the value it extracted.
If they match, it returns true, otherwise false.

OperationEqual simply returns whatever the operation function returns (in this case, that would be OperationEqual).
The first function (Help), checks the return of ParseIf, the function it called to parse the current line, and if true, it parses and executes the line below, otherwise it skips it.

This is a rundown of how it works.

Thank you for so well informed explanation !, it helps. I will look carefully at everything you have described.


> The first function (Help), checks the return of ParseIf, the function it called to parse the current line, and if true, it parses and executes the line below, otherwise it skips it.

I am not 100 % on this one. Does it meen that: if (Number1 == 1) then I can set int i = 4; for example, is this the way it worked. If I get this part then I have all steps from beginning to end to analyze further by myself I think.

Code:

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if ( ParseMap.find( strKeyword.c_str() )->second( strToParse.substr(index + 1) ) )
{   
    int i = 4;        // The if evaluated to true; execute action underneath the if
}
else
                ; // The if evaluated to false; skip everything underneath the if

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This was an example, but you can do something like this:

Code:

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if ( ParseMap.find( strKeyword.c_str() )->second( strToParse.substr(index + 1) ) )
        MessageBox(NULL, "If was true!", "", 0);
else
        MessageBox(NULL, "If was false!", "", 0);

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Now, if I was to change strToParse to this:
if (Numer1 == 4)
What do you think would happen? True or false?

Then it should be false since:

Code:

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VariablesMap["Number1"] = 1;

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wich is the number we compare against. So if we would write 4 there instead, then it will turn True ?
Interpreters is interesting stuff.
:)

Yep, if you put 4 there, it will be true.

Elysia, Great thanks for this help. I will try to develop the examples you have given me and see what I can do with it.