You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
145 lines
7.6 KiB
HTML
145 lines
7.6 KiB
HTML
4 years ago
|
<html lang="en">
|
||
|
|
<head>
|
||
|
|
<title>Differences from previous versions - The C Preprocessor</title>
|
||
|
|
<meta http-equiv="Content-Type" content="text/html">
|
||
|
|
<meta name="description" content="The C Preprocessor">
|
||
|
|
<meta name="generator" content="makeinfo 4.13">
|
||
|
|
<link title="Top" rel="start" href="index.html#Top">
|
||
|
|
<link rel="up" href="Implementation-Details.html#Implementation-Details" title="Implementation Details">
|
||
|
|
<link rel="prev" href="Obsolete-Features.html#Obsolete-Features" title="Obsolete Features">
|
||
|
|
<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
|
||
|
|
<!--
|
||
|
|
Copyright (C) 1987-2015 Free Software Foundation, Inc.
|
||
|
|
|
||
|
|
Permission is granted to copy, distribute and/or modify this document
|
||
|
|
under the terms of the GNU Free Documentation License, Version 1.3 or
|
||
|
|
any later version published by the Free Software Foundation. A copy of
|
||
|
|
the license is included in the
|
||
|
|
section entitled ``GNU Free Documentation License''.
|
||
|
|
|
||
|
|
This manual contains no Invariant Sections. The Front-Cover Texts are
|
||
|
|
(a) (see below), and the Back-Cover Texts are (b) (see below).
|
||
|
|
|
||
|
|
(a) The FSF's Front-Cover Text is:
|
||
|
|
|
||
|
|
A GNU Manual
|
||
|
|
|
||
|
|
(b) The FSF's Back-Cover Text is:
|
||
|
|
|
||
|
|
You have freedom to copy and modify this GNU Manual, like GNU
|
||
|
|
software. Copies published by the Free Software Foundation raise
|
||
|
|
funds for GNU development.
|
||
|
|
-->
|
||
|
|
<meta http-equiv="Content-Style-Type" content="text/css">
|
||
|
|
<style type="text/css"><!--
|
||
|
|
pre.display { font-family:inherit }
|
||
|
|
pre.format { font-family:inherit }
|
||
|
|
pre.smalldisplay { font-family:inherit; font-size:smaller }
|
||
|
|
pre.smallformat { font-family:inherit; font-size:smaller }
|
||
|
|
pre.smallexample { font-size:smaller }
|
||
|
|
pre.smalllisp { font-size:smaller }
|
||
|
|
span.sc { font-variant:small-caps }
|
||
|
|
span.roman { font-family:serif; font-weight:normal; }
|
||
|
|
span.sansserif { font-family:sans-serif; font-weight:normal; }
|
||
|
|
--></style>
|
||
|
|
</head>
|
||
|
|
<body>
|
||
|
|
<div class="node">
|
||
|
|
<a name="Differences-from-previous-versions"></a>
|
||
|
|
<p>
|
||
|
|
Previous: <a rel="previous" accesskey="p" href="Obsolete-Features.html#Obsolete-Features">Obsolete Features</a>,
|
||
|
|
Up: <a rel="up" accesskey="u" href="Implementation-Details.html#Implementation-Details">Implementation Details</a>
|
||
|
|
<hr>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<h3 class="section">11.4 Differences from previous versions</h3>
|
||
|
|
|
||
|
|
<p><a name="index-differences-from-previous-versions-119"></a>
|
||
|
|
This section details behavior which has changed from previous versions
|
||
|
|
of CPP. We do not plan to change it again in the near future, but
|
||
|
|
we do not promise not to, either.
|
||
|
|
|
||
|
|
<p>The “previous versions” discussed here are 2.95 and before. The
|
||
|
|
behavior of GCC 3.0 is mostly the same as the behavior of the widely
|
||
|
|
used 2.96 and 2.97 development snapshots. Where there are differences,
|
||
|
|
they generally represent bugs in the snapshots.
|
||
|
|
|
||
|
|
<ul>
|
||
|
|
<li>-I- deprecated
|
||
|
|
|
||
|
|
<p>This option has been deprecated in 4.0. <samp><span class="option">-iquote</span></samp> is meant to
|
||
|
|
replace the need for this option.
|
||
|
|
|
||
|
|
<li>Order of evaluation of ‘<samp><span class="samp">#</span></samp>’ and ‘<samp><span class="samp">##</span></samp>’ operators
|
||
|
|
|
||
|
|
<p>The standard does not specify the order of evaluation of a chain of
|
||
|
|
‘<samp><span class="samp">##</span></samp>’ operators, nor whether ‘<samp><span class="samp">#</span></samp>’ is evaluated before, after, or
|
||
|
|
at the same time as ‘<samp><span class="samp">##</span></samp>’. You should therefore not write any code
|
||
|
|
which depends on any specific ordering. It is possible to guarantee an
|
||
|
|
ordering, if you need one, by suitable use of nested macros.
|
||
|
|
|
||
|
|
<p>An example of where this might matter is pasting the arguments ‘<samp><span class="samp">1</span></samp>’,
|
||
|
|
‘<samp><span class="samp">e</span></samp>’ and ‘<samp><span class="samp">-2</span></samp>’. This would be fine for left-to-right pasting,
|
||
|
|
but right-to-left pasting would produce an invalid token ‘<samp><span class="samp">e-2</span></samp>’.
|
||
|
|
|
||
|
|
<p>GCC 3.0 evaluates ‘<samp><span class="samp">#</span></samp>’ and ‘<samp><span class="samp">##</span></samp>’ at the same time and strictly
|
||
|
|
left to right. Older versions evaluated all ‘<samp><span class="samp">#</span></samp>’ operators first,
|
||
|
|
then all ‘<samp><span class="samp">##</span></samp>’ operators, in an unreliable order.
|
||
|
|
|
||
|
|
<li>The form of whitespace between tokens in preprocessor output
|
||
|
|
|
||
|
|
<p>See <a href="Preprocessor-Output.html#Preprocessor-Output">Preprocessor Output</a>, for the current textual format. This is
|
||
|
|
also the format used by stringification. Normally, the preprocessor
|
||
|
|
communicates tokens directly to the compiler's parser, and whitespace
|
||
|
|
does not come up at all.
|
||
|
|
|
||
|
|
<p>Older versions of GCC preserved all whitespace provided by the user and
|
||
|
|
inserted lots more whitespace of their own, because they could not
|
||
|
|
accurately predict when extra spaces were needed to prevent accidental
|
||
|
|
token pasting.
|
||
|
|
|
||
|
|
<li>Optional argument when invoking rest argument macros
|
||
|
|
|
||
|
|
<p>As an extension, GCC permits you to omit the variable arguments entirely
|
||
|
|
when you use a variable argument macro. This is forbidden by the 1999 C
|
||
|
|
standard, and will provoke a pedantic warning with GCC 3.0. Previous
|
||
|
|
versions accepted it silently.
|
||
|
|
|
||
|
|
<li>‘<samp><span class="samp">##</span></samp>’ swallowing preceding text in rest argument macros
|
||
|
|
|
||
|
|
<p>Formerly, in a macro expansion, if ‘<samp><span class="samp">##</span></samp>’ appeared before a variable
|
||
|
|
arguments parameter, and the set of tokens specified for that argument
|
||
|
|
in the macro invocation was empty, previous versions of CPP would
|
||
|
|
back up and remove the preceding sequence of non-whitespace characters
|
||
|
|
(<strong>not</strong> the preceding token). This extension is in direct
|
||
|
|
conflict with the 1999 C standard and has been drastically pared back.
|
||
|
|
|
||
|
|
<p>In the current version of the preprocessor, if ‘<samp><span class="samp">##</span></samp>’ appears between
|
||
|
|
a comma and a variable arguments parameter, and the variable argument is
|
||
|
|
omitted entirely, the comma will be removed from the expansion. If the
|
||
|
|
variable argument is empty, or the token before ‘<samp><span class="samp">##</span></samp>’ is not a
|
||
|
|
comma, then ‘<samp><span class="samp">##</span></samp>’ behaves as a normal token paste.
|
||
|
|
|
||
|
|
<li>‘<samp><span class="samp">#line</span></samp>’ and ‘<samp><span class="samp">#include</span></samp>’
|
||
|
|
|
||
|
|
<p>The ‘<samp><span class="samp">#line</span></samp>’ directive used to change GCC's notion of the
|
||
|
|
“directory containing the current file”, used by ‘<samp><span class="samp">#include</span></samp>’ with
|
||
|
|
a double-quoted header file name. In 3.0 and later, it does not.
|
||
|
|
See <a href="Line-Control.html#Line-Control">Line Control</a>, for further explanation.
|
||
|
|
|
||
|
|
<li>Syntax of ‘<samp><span class="samp">#line</span></samp>’
|
||
|
|
|
||
|
|
<p>In GCC 2.95 and previous, the string constant argument to ‘<samp><span class="samp">#line</span></samp>’
|
||
|
|
was treated the same way as the argument to ‘<samp><span class="samp">#include</span></samp>’: backslash
|
||
|
|
escapes were not honored, and the string ended at the second ‘<samp><span class="samp">"</span></samp>’.
|
||
|
|
This is not compliant with the C standard. In GCC 3.0, an attempt was
|
||
|
|
made to correct the behavior, so that the string was treated as a real
|
||
|
|
string constant, but it turned out to be buggy. In 3.1, the bugs have
|
||
|
|
been fixed. (We are not fixing the bugs in 3.0 because they affect
|
||
|
|
relatively few people and the fix is quite invasive.)
|
||
|
|
|
||
|
|
</ul>
|
||
|
|
|
||
|
|
</body></html>
|
||
|
|
|