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Just Another Penguin

string parsing

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Okay, in a game I''m making, the player inputs a command like "move n,10" which is move north 10. How would I parse it in C++? I tried using counters and string arrays, checking for a letter, if it''s there check for the next letter and so on. I know it''s clunky, but could someone enlighten me on a better way?

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How many commands do you got? If you have a very limited num. of commands consider making them simple cases

Case 1 = Move n,1 ;
Case 2 = Move n,2 ;

where you check case n aginst your input string.

Other than that you have to write a simple parser.
In theory first you have to define a grammar. In reallife you have to "separate" the diffrent elements of your grammar/instring then parse them.

Like this:
A = "Move"
B = "n"
C = "1";

to split up the instring use spaces, commas etc to detect a new syntactic particle.

Then, let''s say you defined a simple grammar like this
EXP = A->B->C

This could mean that:
A always be a "Command Type"
B is always one of four directions (n,s,w,e)
C is always an integer.

that gives you a simple grammar like this:

Valid Exp:
CMD -> Direction -> Integer

in reality:

if CMD then Direction
if Direction then integer
return IsValidExp

where CMD = {MOVE, EAT, WALK, JUMP, SURFGAMEDEV}
DIRECTION {EAST,E,NORTH,N,SOUTH,S}
INTEGER {1..100}

Parsers are not that complex as they may seem. What makes them kinda hard to get is getting used to the notation used when defining a grammar. Also the most common parser is called a "recursive descent" parser...which parses a string in a recursive manner. And as you may know recursive algorithms can be a real b*tch...

Parsers are a big thing in cs...the www is flooded with stuff about how to write and design em''.

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I don''t use them, but I remember there are some commands that only read in one word, and stop at a space. You could use those (fin, or something like that?) and the strcmp function to check commands also.

Just figured I''d present another option. Hopefully I''m not too inaccurate.

-Arek the Absolute

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