Reading from file: without escape Backslash
Thomas Guettler
I have a lisp program which reads with
(setq *gefa-prog-dir* (pathname (read infile))
*gefa-ext-prog-dir* (pathname (read infile))))
data from a file. The file looks like this:
"C:\\xuma\\"
"C:\\xuma\\gefa\\daten\\"
But unfortunately a different programm (installer) needs
these paths, too. But the installer want it to be with
only one backslash. I looked at the help of "read" but there
is no option for turning backslash interpretion off.
I will try to write a method which reads character by character,
but may be someone has a better solution?
Thank you
thomas
Tim Bradshaw
> I will try to write a method which reads character by character,
> but may be someone has a better solution?
don't quote the strings and use READ-LINE?
--tim
Adam Warner
> data from a file. The file looks like this:
> "C:\\xuma\\"
> "C:\\xuma\\gefa\\daten\\"
The file only looks like that because you are writing the output with the
escape characters. Backslash is an escape character so to display a
backslash it has to be backslashed. You could print out the strings using
princ instead of write. Compare the difference by evaluating these:
(write "C:\\xuma\\gefa\\daten\\")
(princ "C:\\xuma\\gefa\\daten\\")
Write prints output that in a form that can (typically) be read back in.
There's a lot more to the Lisp printer:
http://www.lispworks.com/reference/HyperSpec/Body/22_.htm
Regards,
Adam
Adam Warner
> data from a file. The file looks like this:
> "C:\\xuma\\"
> "C:\\xuma\\gefa\\daten\\"
Perhaps the file only looks like that because you are writing the output
with the escape characters. Backslash is an escape character so to display a
backslash it has to be backslashed. You could print out the strings using
princ instead of write. Compare the difference by evaluating these:
(write "C:\\xuma\\gefa\\daten\\")
(princ "C:\\xuma\\gefa\\daten\\")
Write prints output in a form that can (typically) be read back in.
Thomas Guettler
> Hi Thomas Guettler,
>
>
>>data from a file. The file looks like this:
>>"C:\\xuma\\"
>>"C:\\xuma\\gefa\\daten\\"
> Write prints output in a form that can (typically) be read back in.
But isn't \n a newline?
thomas
Adam Warner
> But isn't \n a newline?
No, \n is the character n. You can see this from a Lisp console:
[1]> "\n"
"n"
Newlines in Lisp strings are typed in as actual newlines:
[2]> "line1
line2"
"line1
line2"
You cannot express them using escape notation.
If you are concatenating a string just take the string of the newline
character:
[3]> (concatenate 'string "line1" (string #\Newline) "line2")
"line1
line2"
Which is exactly the same output as above.
A more compact way is using the format function:
[4]> (format nil "line1~%line2")
"line1
line2"
t prints (it doesn't just return a string):
[5]> (format t "line1~%line2")
line1
line2
You can can even produce multiple newlines:
[6]> (format t "line1~5%line2")
line1
line2
Regards,
Adam
Erik Naggum
| But isn't \n a newline?
In Common Lisp, \ in strings only really escapes the " that would terminate
the string, but since there is a need for an escape character, also itself.
Another way to do this would be let two delimiters become one, but that was
a path not taken for Common Lisp. The reason for this is that \ is useful
to make certain that any character is really a constituent in the print name
of symbols. Note that Common Lisp has both a single-escape and a
multiple-escape mechanism with \ and |, respectively. The latter, however,
also makes letters retain their case, so the decision to use | over \ also
has to be balanced for aesthetics. There is nothing syntactically wrong in
writing code |with| |symbols| |like| |this|, but it tends to get on people's
nerves.
--
Erik Naggum, Oslo, Norway
Act from reason, and failure makes you rethink and study harder.
Act from faith, and failure makes you blame someone and push harder.