Path: utzoo!news-server.csri.toronto.edu!rutgers!ucsd!sdd.hp.com!think.com!barmar
From: barmar@think.com (Barry Margolin)
Newsgroups: comp.lang.lisp
Subject: Re: strings with escape characters
Keywords: strings, escape characters
Message-ID: <1991Mar15.184822.17411@Think.COM>
Date: 15 Mar 91 18:48:22 GMT
References: <27E0EDEE.49E5@ibma0.cs.uiuc.edu>
Sender: news@Think.COM
Organization: Thinking Machines Corporation, Cambridge MA, USA
Lines: 43

In article <27E0EDEE.49E5@ibma0.cs.uiuc.edu> murphy@ibma0.cs.uiuc.edu (michael r murphy) writes:
>I would like to read in a C string and keep the escape characters 
>as is.  I have enclosed a sample of my problem.  What I would like
>is:
>
><cl> (setf foo "\nThis is a c string\n")
>
>"\nThis is a c string\n"
>
>I just want to get the \ in there without it being interpreted as 
>an escape.  I can then handle printing it out.  Help.

You have to double the slash, i.e.

(setf foo "\\nThis is a c string\\n")

><cl> (setf foo |"\nThis is a c string\n"|)
>Error: Attempt to take the value of the unbound symbol |"nThis is a c stringn"|

|...| is a symbol, not a string, so you have to use single-quote to prevent
it from being evaluated.  Also, backslash is interpreted inside vertical
bars (to allow you to include a vertical bar as a character in a symbol
name), so you still have to double it:

(setf foo '|"\\nThis is a c string\\n"|)

Note that in both cases there is only one backslash in the actual string.
The doubling is only necessary during I/O.  Notice:

> (setq *string* "\\n")
"\\n"
> (length *string*)
2
> (coerce *string* 'list)
(#\\ #\n)
> (write-string *string*)
\n
"\\n"
--
Barry Margolin, Thinking Machines Corp.

barmar@think.com
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