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<a name="Pseudo-Arguments"></a>
<div class="header">
<p>
Next: <a href="Undefine.html#Undefine" accesskey="n" rel="next">Undefine</a>, Previous: <a href="Arguments.html#Arguments" accesskey="p" rel="prev">Arguments</a>, Up: <a href="Definitions.html#Definitions" accesskey="u" rel="up">Definitions</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Indices.html#Indices" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="Special-arguments-to-macros"></a>
<h3 class="section">5.3 Special arguments to macros</h3>

<a name="index-special-arguments-to-macros"></a>
<a name="index-macros_002c-special-arguments-to"></a>
<a name="index-arguments-to-macros_002c-special"></a>
<p>There is a special notation for the number of actual arguments supplied,
and for all the actual arguments.
</p>
<p>The number of actual arguments in a macro call is denoted by <code>$#</code>
in the expansion text.
</p>
<dl>
<dt><a name="index-nargs"></a>Composite: <strong>nargs</strong> <em>(&hellip;)</em></dt>
<dd><p>Expands to a count of the number of arguments supplied.
</p></dd></dl>

<div class="example">
<pre class="example">define(`nargs', `$#')
&rArr;
nargs
&rArr;0
nargs()
&rArr;1
nargs(`arg1', `arg2', `arg3')
&rArr;3
nargs(`commas can be quoted, like this')
&rArr;1
nargs(arg1#inside comments, commas do not separate arguments
still arg1)
&rArr;1
nargs((unquoted parentheses, like this, group arguments))
&rArr;1
</pre></div>

<p>Remember that &lsquo;<samp>#</samp>&rsquo; defaults to the comment character; if you forget
quotes to inhibit the comment behavior, your macro definition may not
end where you expected.
</p>
<div class="example">
<pre class="example">dnl Attempt to define a macro to just `$#'
define(underquoted, $#)
oops)
&rArr;
underquoted
&rArr;0)
&rArr;oops
</pre></div>

<p>The notation <code>$*</code> can be used in the expansion text to denote all
the actual arguments, unquoted, with commas in between.  For example
</p>
<div class="example">
<pre class="example">define(`echo', `$*')
&rArr;
echo(arg1,    arg2, arg3 , arg4)
&rArr;arg1,arg2,arg3 ,arg4
</pre></div>

<p>Often each argument should be quoted, and the notation <code>$@</code> handles
that.  It is just like <code>$*</code>, except that it quotes each argument.
A simple example of that is:
</p>
<div class="example">
<pre class="example">define(`echo', `$@')
&rArr;
echo(arg1,    arg2, arg3 , arg4)
&rArr;arg1,arg2,arg3 ,arg4
</pre></div>

<p>Where did the quotes go?  Of course, they were eaten, when the expanded
text were reread by <code>m4</code>.  To show the difference, try
</p>
<div class="example">
<pre class="example">define(`echo1', `$*')
&rArr;
define(`echo2', `$@')
&rArr;
define(`foo', `This is macro `foo'.')
&rArr;
echo1(foo)
&rArr;This is macro This is macro foo..
echo1(`foo')
&rArr;This is macro foo.
echo2(foo)
&rArr;This is macro foo.
echo2(`foo')
&rArr;foo
</pre></div>

<p>See <a href="Trace.html#Trace">Trace</a>, if you do not understand this.  As another example of the
difference, remember that comments encountered in arguments are passed
untouched to the macro, and that quoting disables comments.
</p>
<div class="example">
<pre class="example">define(`echo1', `$*')
&rArr;
define(`echo2', `$@')
&rArr;
define(`foo', `bar')
&rArr;
echo1(#foo'foo
foo)
&rArr;#foo'foo
&rArr;bar
echo2(#foo'foo
foo)
&rArr;#foobar
&rArr;bar'
</pre></div>


<p>A &lsquo;<samp>$</samp>&rsquo; sign in the expansion text, that is not followed by anything
<code>m4</code> understands, is simply copied to the macro expansion, as any
other text is.
</p>
<div class="example">
<pre class="example">define(`foo', `$$$ hello $$$')
&rArr;
foo
&rArr;$$$ hello $$$
</pre></div>

<a name="index-rescanning-2"></a>
<a name="index-literal-output"></a>
<a name="index-output_002c-literal"></a>
<p>If you want a macro to expand to something like &lsquo;<samp>$12</samp>&rsquo;, the
judicious use of nested quoting can put a safe character between the
<code>$</code> and the next character, relying on the rescanning to remove the
nested quote.  This will prevent <code>m4</code> from interpreting the
<code>$</code> sign as a reference to an argument.
</p>
<div class="example">
<pre class="example">define(`foo', `no nested quote: $1')
&rArr;
foo(`arg')
&rArr;no nested quote: arg
define(`foo', `nested quote around $: `$'1')
&rArr;
foo(`arg')
&rArr;nested quote around $: $1
define(`foo', `nested empty quote after $: $`'1')
&rArr;
foo(`arg')
&rArr;nested empty quote after $: $1
define(`foo', `nested quote around next character: $`1'')
&rArr;
foo(`arg')
&rArr;nested quote around next character: $1
define(`foo', `nested quote around both: `$1'')
&rArr;
foo(`arg')
&rArr;nested quote around both: arg
</pre></div>

<hr>
<div class="header">
<p>
Next: <a href="Undefine.html#Undefine" accesskey="n" rel="next">Undefine</a>, Previous: <a href="Arguments.html#Arguments" accesskey="p" rel="prev">Arguments</a>, Up: <a href="Definitions.html#Definitions" accesskey="u" rel="up">Definitions</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Indices.html#Indices" title="Index" rel="index">Index</a>]</p>
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m4-doc 1.4.18-1 / usr / share / doc / m4-doc / Pseudo-Arguments.html
