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Documented %xdefine and %xidefine, and fixed an index item in %define.

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Debbie Wiles 2002-05-25 13:12:21 +00:00
parent 64de47c0cb
commit 64fee5a6c8
1 changed files with 47 additions and 1 deletions
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doc/nasmdoc.src
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@ -1749,6 +1749,52 @@ You can \i{pre-define} single-line macros using the `-d' option on
the NASM command line: see \k{opt-d}.
\S{xdefine} Enhancing %define: \I\c{%xidefine}\i\c{%xdefine}
To have a reference to an embedded single-line macro resolved at the
time that it is embedded, as opposed to when the calling macro is
expanded, you need a different mechanism to the one offered by
\c{%define}. The solution is to use \c{%xdefine}, or it's
\I{case sensitive}case-insensitive counterpart \c{%xidefine}.
Suppose you have the following code:
\c %define isTrue 1
\c %define isFalse isTrue
\c %define isTrue 0
\c
\c val1: db isFalse
\c
\c %define isTrue 1
\c
\c val2: db isFalse
In this case, \c{val1} is equal to 0, and \c{val2} is equal to 1.
This is because, when a single-line macro is defined using
\c{%define}, it is expanded only when it is called. As \c{isFalse}
expands to \c{isTrue}, the expansion will be the current value of
\c{isTrue}. The first time it is called that is 0, and the second
time it is 1.
If you wanted \c{isFalse} to expand to the value assigned to the
embedded macro \c{isTrue} at the time that \c{isFalse} was defined,
you need to change the above code to use \c{%xdefine}.
\c %xdefine isTrue 1
\c %xdefine isFalse isTrue
\c %xdefine isTrue 0
\c
\c val1: db isFalse
\c
\c %xdefine isTrue 1
\c
\c val2: db isFalse
Now, each time that \c{isFalse} is called, it expands to 1,
as that is what the embedded macro \c{isTrue} expanded to at
the time that \c{isFalse} was defined.
\S{concat%+} Concatenating Single Line Macro Tokens: \i\c{%+}
Individual tokens in single line macros can be concatenated, to produce
@ -1808,7 +1854,7 @@ command-line using the `-u' option on the NASM command line: see
\S{assign} \i{Preprocessor Variables}: \i\c{%assign}
An alternative way to define single-line macros is by means of the
\c{%assign} command (and its \i{case sensitive}case-insensitive
\c{%assign} command (and its \I{case sensitive}case-insensitive
counterpart \i\c{%iassign}, which differs from \c{%assign} in
exactly the same way that \c{%idefine} differs from \c{%define}).