| Topic: |
DEVELOP > c-Plus-Plus |
| User: |
"kill sunday" |
| Date: |
19 Oct 2003 11:17:54 AM |
| Object: |
cin.peek() |
I'm working on an RPN calculator, and i can't get the input right.
I have to use cin.peek() to check the next character and do whatever i need
with it. I can't get it to look for a specific type of data. i need it to
look and see if its a double, whitespace or an operator. any suggestions?
david crean
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| User: "Jerry Coffin" |
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| Title: Re: cin.peek() |
21 Oct 2003 11:05:37 AM |
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In article <bmudiu$qnedv$1@ID-183738.news.uni-berlin.de>,
david@manicelement.com says...
I'm working on an RPN calculator, and i can't get the input right.
I have to use cin.peek() to check the next character and do whatever i need
with it. I can't get it to look for a specific type of data. i need it to
look and see if its a double, whitespace or an operator. any suggestions?
First, I'd advise using an iterator for the input instead of explicitly
reading from a stream -- this will allow you (for example) to parse a
string instead of a stream.
Second, you can't (for one example) determine whether something is a
double using cin.peek -- you get to peek one character ahead, which
would allow you to check whether it's a character that would be part of
a double, but that's about it.
Normally, you want to separate things into a couple of pieces (basically
a lexer and a parser), one of which reads tokens from the input, and the
other of which deals with the expression they form. At least when I've
done it, I've never used peek -- I usually just read characters in, and
when I've gone one too far, I push a character back. Clearly you could
use peek instead, but either way you'll have to deal with things its
way: what you read will always be a character. From there, determining
the 'type' is typically based on the character classification functions
from ctype (e.g. isdigit will help determine whether you're reading a
number).
--
Later,
Jerry.
The universe is a figment of its own imagination.
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