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Re: why doesn't this macro work!?
From: |
Eric Blake |
Subject: |
Re: why doesn't this macro work!? |
Date: |
Sun, 08 Mar 2009 08:40:31 -0600 |
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Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.19) Gecko/20081209 Thunderbird/2.0.0.19 Mnenhy/0.7.6.666 |
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Please don't top-post on technical lists.
According to John Wohlbier on 3/8/2009 12:42 AM:
>> but other variations give me
>> -DDBC=\$withval
>> -DDBC=\$DBC
>>
>> AC_MSG_NOTICE([setting level of DBC to $withval])
>> AC_DEFINE(DBC, $withval)
> Of course I figured it out the minute after I sent the mail.
> AC_DEFINE_UNQUOTED.
> I can't claim to understand exactly why, but it works.
AC_DEFINE behaves as if it is part of a quoted shell here-doc (cat
<<\EOF), hence things such as $ are taken literally. AC_DEFINE_UNQUOTED
behaves as if it is part of an unquoted shell her-doc (cat <<EOF), so
variable expansions can occur. Thus, any time you want shell expansions,
you are correct that you have to use the alternate macro.
Meanwhile, you are missing recommended m4 quoting; the better way to write
this would be:
AC_DEFINE_UNQUOTED([DBC], [$withval])
- --
Don't work too hard, make some time for fun as well!
Eric Blake address@hidden
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