OpenCores
URL https://opencores.org/ocsvn/openrisc_me/openrisc_me/trunk

Subversion Repositories openrisc_me

[/] [openrisc/] [trunk/] [gnu-src/] [gcc-4.2.2/] [faq.html] - Diff between revs 38 and 154

Go to most recent revision | Show entire file | Details | Blame | View Log

Rev 38 Rev 154
Line 1... Line 1...
 
<html>
 
 
 
<head>
 
<title>GCC Frequently Asked Questions</title>
 
</head>
 
 
 
<body>
 
 
 
<h1>GCC Frequently Asked Questions</h1>
 
 
 
<p>The latest version of this document is always available at
 
<a href="http://gcc.gnu.org/faq.html">http://gcc.gnu.org/faq.html</a>.</p>
 
 
 
<p>This FAQ tries to answer specific questions concerning GCC. For
 
general information regarding C, C++, resp. Fortran please check the
 
<a href="http://c-faq.com/">comp.lang.c FAQ</a>,
 
<a href="http://www.comeaucomputing.com/csc/faq.html">comp.std.c++
 
FAQ</a>,
 
and the <a href="http://www.fortran.com/fortran/info.html">Fortran
 
Information page</a>.</p>
 
 
 
<p>Other GCC-related FAQs:
 
   <a href="http://gcc.gnu.org/onlinedocs/libstdc++/faq/index.html">
 
     libstdc++-v3</a>, and
 
   <a href="http://gcc.gnu.org/java/faq.html">GCJ</a>.</p>
 
 
 
<hr />
 
<h1>Questions</h1>
 
<ol>
 
  <li><a href="#general">General information</a>
 
  <ol>
 
     <li><a href="#support">How do I get a bug fixed or a feature added?</a></li>
 
     <li><a href="#platforms">Does GCC work on my platform?</a></li>
 
  </ol></li>
 
 
 
  <li><a href="#installation">Installation</a>
 
  <ol>
 
    <li><a href="#multiple">How to install multiple versions of GCC</a></li>
 
    <li><a href="#rpath">Dynamic linker is unable to find GCC libraries</a></li>
 
    <li><a href="#rpath">libstdc++/libio tests fail badly with --enable-shared</a></li>
 
    <li><a href="#gas">GCC can not find GNU as/GNU ld</a></li>
 
    <li><a href="#environ">cpp: Usage:... Error</a></li>
 
    <li><a href="#optimizing">Optimizing the compiler itself</a></li>
 
    <li><a href="#iconv">Why does <code>libiconv</code> get linked into <code>jc1</code> on Solaris?</a></li>
 
  </ol></li>
 
 
 
  <li><a href="#testsuite">Testsuite problems</a>
 
  <ol>
 
    <li><a href="#testoptions">How do I pass flags like
 
        <code>-fnew-abi</code> to the testsuite?</a></li>
 
    <li><a href="#multipletests">How can I run the test suite with multiple options?</a></li>
 
  </ol></li>
 
 
 
  <li><a href="#misc">Miscellaneous</a>
 
  <ol>
 
    <li><a href="#friend">Friend Templates</a></li>
 
    <li><a href="#dso"><code>dynamic_cast</code>, <code>throw</code>, <code>typeid</code> don't work with shared libraries</a></li>
 
    <li><a href="#generated_files">Why do I need autoconf, bison, xgettext, automake, etc?</a></li>
 
    <li><a href="#picflag-needed">Why can't I build a shared library?</a></li>
 
    <li><a href="#vtables">When building C++, the linker says my constructors, destructors or virtual tables are undefined, but I defined them</a></li>
 
  </ol></li>
 
</ol>
 
 
 
 
 
<hr />
 
<a name="general"></a>
 
<h1>General information</h1>
 
 
 
<!-- The "bugreport" anchor was used in ICE messages of GCC < 2.95.3. -->
 
<h2 id="bugreport"><a name="support">How do I get a bug fixed or
 
    a feature added?</a></h2>
 
 
 
<p>There are lots of ways to get something fixed.  The list below may be
 
incomplete, but it covers many of the common cases.  These are listed
 
roughly in order of decreasing difficulty for the average GCC user,
 
meaning someone who is not skilled in the internals of GCC, and where
 
difficulty is measured in terms of the time required to fix the bug.
 
No alternative is better than any other; each has its benefits and
 
disadvantages.</p>
 
 
 
<ul>
 
<li>Fix it yourself.  This alternative will probably bring results,
 
    if you work hard enough, but will probably take a lot of time,
 
    and, depending on the quality of your work and the perceived
 
    benefits of your changes, your code may or may not ever make it
 
    into an official release of GCC.</li>
 
 
 
<li><a href="bugs.html">Report the problem to the GCC bug tracking system</a>
 
    and hope that someone will be kind
 
    enough to fix it for you.  While this is certainly possible, and
 
    often happens, there is no guarantee that it will.  You should
 
    not expect the same response from this method that you would see
 
    from a commercial support organization since the people who read
 
    GCC bug reports, if they choose to help you, will be volunteering their
 
    time.</li>
 
 
 
<li>Hire someone to fix it for you.  There are various companies and
 
    individuals providing support for GCC.  This alternative costs
 
    money, but is relatively likely to get results.</li>
 
</ul>
 
 
 
<hr />
 
<h2><a name="platforms">Does GCC work on my platform?</a></h2>
 
 
 
<p>The host/target specific installation notes for GCC include information
 
about known problems with installing or using GCC on particular platforms.
 
These are included in the sources for a release in INSTALL/specific.html,
 
and the <a href="http://gcc.gnu.org/install/specific.html">latest version</a>
 
is always available at the GCC web site.
 
Reports of <a href="http://gcc.gnu.org/buildstat.html">successful builds</a>
 
for several versions of GCC are also available at the web site.</p>
 
 
 
<hr />
 
<a name="installation"></a>
 
<h1>Installation</h1>
 
 
 
<h2><a name="multiple">How to install multiple versions of GCC</a></h2>
 
 
 
<p>It may be desirable to install multiple versions of the compiler on
 
the same system.  This can be done by using different prefix paths at
 
configure time and a few symlinks.</p>
 
 
 
<p>Basically, configure the two compilers with different --prefix options,
 
then build and install each compiler.  Assume you want "gcc" to be the latest
 
compiler and available in /usr/local/bin; also assume that you want "gcc2"
 
to be the older gcc2 compiler and also available in /usr/local/bin.</p>
 
 
 
<p>The easiest way to do this is to configure the new GCC with
 
<code>--prefix=/usr/local/gcc</code> and the older gcc2 with
 
<code>--prefix=/usr/local/gcc2</code>.  Build and install both
 
compilers.  Then make a symlink from <code>/usr/local/bin/gcc</code>
 
to <code>/usr/local/gcc/bin/gcc</code> and from
 
<code>/usr/local/bin/gcc2</code> to
 
<code>/usr/local/gcc2/bin/gcc</code>.  Create similar links for the
 
"g++", "c++" and "g77" compiler drivers.</p>
 
 
 
<p>An alternative to using symlinks is to configure with a
 
<code>--program-transform-name</code> option. This option specifies a
 
sed command to process installed program names with. Using it you can,
 
for instance, have all the new GCC programs installed as "new-gcc" and
 
the like. You will still have to specify different
 
<code>--prefix</code> options for new GCC and old GCC, because it is
 
only the executable program names that are transformed. The difference
 
is that you (as administrator) do not have to set up symlinks, but
 
must specify additional directories in your (as a user) PATH. A
 
complication with <code>--program-transform-name</code> is that the
 
sed command invariably contains characters significant to the shell,
 
and these have to be escaped correctly, also it is not possible to use
 
"^" or "$" in the command. Here is the option to prefix "new-" to the
 
new GCC installed programs:</p>
 
<blockquote><code>
 
--program-transform-name='s,\\\\(.*\\\\),new-\\\\1,'
 
</code></blockquote>
 
<p>With the above <code>--prefix</code> option, that will install the new
 
GCC programs into <code>/usr/local/gcc/bin</code> with names prefixed
 
by "new-". You can use <code>--program-transform-name</code> if you
 
have multiple versions of GCC, and wish to be sure about which version
 
you are invoking.</p>
 
 
 
<p>If you use <code>--prefix</code>, GCC may have difficulty locating a GNU
 
assembler or linker on your system, <a href="#gas">GCC can not find GNU
 
as/GNU ld</a> explains how to deal with this.</p>
 
 
 
<p>Another option that may be easier is to use the
 
<code>--program-prefix=</code> or <code>--program-suffix=</code>
 
options to configure. So if you're installing GCC 2.95.2 and don't
 
want to disturb the current version of GCC in
 
<code>/usr/local/bin/</code>, you could do</p>
 
<blockquote><code>
 
configure --program-suffix=-2.95.2 &lt;other configure options&gt;
 
</code></blockquote>
 
<p>This should result in GCC being installed as
 
<code>/usr/local/bin/gcc-2.95.2</code> instead of
 
<code>/usr/local/bin/gcc</code>.</p>
 
 
 
<hr />
 
<h2><a name="rpath">Dynamic linker is unable to find GCC libraries</a></h2>
 
 
 
<p>This problem manifests itself by programs not finding shared
 
libraries they depend on when the programs are started.  Note this
 
problem often manifests itself with failures in the libio/libstdc++
 
tests after configuring with <code>--enable-shared</code> and building GCC.</p>
 
 
 
<p>GCC does not specify a runpath so that the dynamic linker can find
 
dynamic libraries at runtime.</p>
 
 
 
<p>The short explanation is that if you always pass a -R option to the
 
linker, then your programs become dependent on directories which
 
may be NFS mounted, and programs may hang unnecessarily when an
 
NFS server goes down.</p>
 
 
 
<p>The problem is not programs that do require the directories; those
 
programs are going to hang no matter what you do.  The problem is
 
programs that do not require the directories.</p>
 
 
 
<p>SunOS effectively always passed a <code>-R</code> option for every
 
<code>-L</code> option; this was a bad idea, and so it was removed for
 
Solaris.  We should not recreate it.</p>
 
 
 
<p>However, if you feel you really need such an option to be passed
 
automatically to the linker, you may add it to the GCC specs file.
 
This file can be found in the same directory that contains cc1 (run
 
<code>gcc -print-prog-name=cc1</code> to find it).  You may add linker
 
flags such as <code>-R</code> or <code>-rpath</code>, depending on
 
platform and linker, to the <code>*link</code> or <code>*lib</code>
 
specs.</p>
 
 
 
<p>Another alternative is to install a wrapper script around gcc, g++
 
or ld that adds the appropriate directory to the environment variable
 
<code>LD_RUN_PATH</code> or equivalent (again, it's
 
platform-dependent).</p>
 
 
 
<p>Yet another option, that works on a few platforms, is to hard-code
 
the full pathname of the library into its soname.  This can only be
 
accomplished by modifying the appropriate <tt>.ml</tt> file within
 
<tt>libstdc++/config</tt> (and also <tt>libg++/config</tt>, if you are
 
building libg++), so that <code>$(libdir)/</code> appears just before
 
the library name in <code>-soname</code> or <code>-h</code> options.</p>
 
 
 
<hr />
 
<h2><a name="gas">GCC can not find GNU as/GNU ld</a></h2>
 
<p>GCC searches the PATH for an assembler and a loader, but it only
 
does so after searching a directory list hard-coded in the GCC
 
executables.  Since, on most platforms, the hard-coded list includes
 
directories in which the system assembler and loader can be found, you
 
may have to take one of the following actions to arrange that GCC uses
 
the GNU versions of those programs.</p>
 
 
 
<p>To ensure that GCC finds the GNU assembler (the GNU loader), which
 
are required by <a href="http://gcc.gnu.org/install/specific.html">some
 
configurations</a>,
 
you should configure these with the same --prefix option as you used
 
for GCC.  Then build &amp; install GNU as (GNU ld) and proceed with
 
building GCC.</p>
 
 
 
<p>Another alternative is to create links to GNU as and ld in any of
 
the directories printed by the command `<tt>gcc -print-search-dirs |
 
grep '^programs:'</tt>'.  The link to `<tt>ld</tt>' should be named
 
`<tt>real-ld</tt>' if `<tt>ld</tt>' already exists.  If such links do
 
not exist while you're compiling GCC, you may have to create them in
 
the build directories too, within the <tt>gcc</tt> directory
 
<em>and</em> in all the <tt>gcc/stage*</tt> subdirectories.</p>
 
 
 
<p>GCC 2.95 allows you to specify the full pathname of the assembler
 
and the linker to use.  The configure flags are
 
`<tt>--with-as=/path/to/as</tt>' and `<tt>--with-ld=/path/to/ld</tt>'.
 
GCC will try to use these pathnames before looking for `<tt>as</tt>'
 
or `<tt>(real-)ld</tt>' in the standard search dirs.  If, at
 
configure-time, the specified programs are found to be GNU utilities,
 
`<tt>--with-gnu-as</tt>' and `<tt>--with-gnu-ld</tt>' need not be
 
used; these flags will be auto-detected.  One drawback of this option
 
is that it won't allow you to override the search path for assembler
 
and linker with command-line options <tt>-B/path/</tt> if the
 
specified filenames exist.</p>
 
 
 
<hr />
 
<h2><a name="environ">cpp: Usage:... Error</a></h2>
 
 
 
<p>If you get an error like this when building GCC (particularly when building
 
__mulsi3), then you likely have a problem with your environment variables.</p>
 
<pre>
 
  cpp: Usage: /usr/lib/gcc-lib/i586-unknown-linux-gnulibc1/2.7.2.3/cpp
 
  [switches] input output
 
</pre>
 
<p>First look for an explicit '.' in either LIBRARY_PATH or GCC_EXEC_PREFIX
 
from your environment.  If you do not find an explicit '.', look for
 
an empty pathname in those variables.  Note that ':' at either the start
 
or end of these variables is an implicit '.' and will cause problems.</p>
 
 
 
<p>Also note '::' in these paths will also cause similar problems.</p>
 
 
 
 
 
<hr />
 
<h2><a name="optimizing">Optimizing the compiler itself</a></h2>
 
 
 
<p>If you want to test a particular optimization option, it's useful to try
 
bootstrapping the compiler with that option turned on.  For example, to
 
test the <code>-fssa</code> option, you could bootstrap like this:</p>
 
 
 
<pre>make BOOT_CFLAGS="-O2 -fssa" bootstrap</pre>
 
 
 
<hr />
 
<h2><a name="iconv">Why does <code>libiconv</code> get linked into <code>jc1</code> on Solaris?</a></h2>
 
 
 
<p>The Java front end requires <code>iconv</code>.  If the compiler
 
used to bootstrap GCC finds <code>libiconv</code> (because the GNU
 
version of <code>libiconv</code> has been installed in the same prefix
 
as the bootstrap compiler), but the newly built GCC does not find the
 
library (because it will be installed with a different prefix), then a
 
link-time error will occur when building <code>jc1</code>.  This
 
problem does not show up so often on platforms that have
 
<code>libiconv</code> in a default location (like
 
<code>/usr/lib</code>) because then both compilers can find a library
 
named <code>libiconv</code>, even though it is a different
 
library.</p>
 
 
 
<p>Using <code>--disable-nls</code> at configure-time does not
 
prevent this problem because <code>jc1</code> uses
 
<code>iconv</code> even in that case.  Solutions include temporarily
 
removing the GNU <code>libiconv</code>, copying it to a default
 
location such as <code>/usr/lib/</code>, and using
 
<code>--enable-languages</code> at configure-time to disable Java.</p>
 
 
 
<hr />
 
<a name="testsuite"></a>
 
<h1>Testsuite problems</h1>
 
 
 
<h2><a name="testoptions">How do I pass flags like
 
  <code>-fnew-abi</code> to the testsuite?</a></h2>
 
 
 
<p>If you invoke <code>runtest</code> directly, you can use the
 
<code>--tool_opts</code> option, e.g:</p>
 
<pre>
 
  runtest --tool_opts "-fnew-abi -fno-honor-std" &lt;other options&gt;
 
</pre>
 
<p>Or, if you use <code>make check</code> you can use the
 
<code>make</code> variable <code>RUNTESTFLAGS</code>, e.g:</p>
 
<pre>
 
  make RUNTESTFLAGS="--tool_opts '-fnew-abi -fno-honor-std'" check-g++
 
</pre>
 
 
 
<hr />
 
<h2><a name="multipletests"> How can I run the test suite with multiple options? </a></h2>
 
 
 
<p>If you invoke <code>runtest</code> directly, you can use the
 
<code>--target_board</code> option, e.g:</p>
 
<pre>
 
  runtest --target_board "unix{-fPIC,-fpic,}" &lt;other options&gt;
 
</pre>
 
<p>Or, if you use <code>make check</code> you can use the
 
<code>make</code> variable <code>RUNTESTFLAGS</code>, e.g:</p>
 
<pre>
 
  make RUNTESTFLAGS="--target_board 'unix{-fPIC,-fpic,}'" check-gcc
 
</pre>
 
<p>Either of these examples will run the tests three times.   Once
 
with <code>-fPIC</code>, once with <code>-fpic</code>, and once with
 
no additional flags.</p>
 
 
 
<p>This technique is particularly useful on multilibbed targets.</p>
 
 
 
 
 
<hr />
 
<a name="misc"></a>
 
<h1>Miscellaneous</h1>
 
 
 
 
 
<h2><a name="friend">Friend Templates</a></h2>
 
 
 
<p>In order to make a specialization of a template function a friend
 
of a (possibly template) class, you must explicitly state that the
 
friend function is a template, by appending angle brackets to its
 
name, and this template function must have been declared already.
 
Here's an example:</p>
 
<pre>
 
template &lt;typename T&gt; class foo {
 
  friend void bar(foo&lt;T&gt;);
 
}
 
</pre>
 
<p>The above declaration declares a non-template function named
 
<code>bar</code>, so it must be explicitly defined for <b>each</b>
 
specialization of <code>foo</code>.  A template definition of <code>bar</code>
 
won't do, because it is unrelated with the non-template declaration
 
above.  So you'd have to end up writing:</p>
 
<pre>
 
void bar(foo&lt;int&gt;) { /* ... */ }
 
void bar(foo&lt;void&gt;) { /* ... */ }
 
</pre>
 
<p>If you meant <code>bar</code> to be a template function, you should
 
have forward-declared it as follows.  Note that, since the template
 
function declaration refers to the template class, the template class
 
must be forward-declared too:</p>
 
<pre>
 
template &lt;typename T&gt;
 
class foo;
 
 
 
template &lt;typename T&gt;
 
void bar(foo&lt;T&gt;);
 
 
 
template &lt;typename T&gt;
 
class foo {
 
  friend void bar&lt;&gt;(foo&lt;T&gt;);
 
};
 
 
 
template &lt;typename T&gt;
 
void bar(foo&lt;T&gt;) { /* ... */ }
 
</pre>
 
<p>In this case, the template argument list could be left empty,
 
because it can be implicitly deduced from the function arguments, but
 
the angle brackets must be present, otherwise the declaration will be
 
taken as a non-template function.  Furthermore, in some cases, you may
 
have to explicitly specify the template arguments, to remove
 
ambiguity.</p>
 
 
 
<p>An error in the last public comment draft of the ANSI/ISO C++
 
Standard and the fact that previous releases of GCC would accept such
 
friend declarations as template declarations has led people to believe
 
that the forward declaration was not necessary, but, according to the
 
final version of the Standard, it is.</p>
 
 
 
 
 
<hr />
 
<h2><a name="dso"><code>dynamic_cast</code>, <code>throw</code>, <code>typeid</code> don't work with shared libraries</a></h2>
 
 
 
<p>The new C++ ABI in the GCC 3.0 series uses address comparisons,
 
rather than string compares, to determine type equality.  This leads
 
to better performance.  Like other objects that have to be present in the
 
final executable, these <code>std::type_info</code> objects have what
 
is called vague linkage because they are not tightly bound to any one
 
particular translation unit (object file).  The compiler has to emit
 
them in any translation unit that requires their presence, and then
 
rely on the linking and loading process to make sure that only one of
 
them is active in the final executable.  With static linking all of
 
these symbols are resolved at link time, but with dynamic linking,
 
further resolution occurs at load time.  You have to ensure that
 
objects within a shared library are resolved against objects in the
 
executable and other shared libraries.</p>
 
 
 
<ul>
 
<li>For a program which is linked against a shared library, no additional
 
precautions are needed.</li>
 
 
 
<li>You cannot create a shared library with the "<code>-Bsymbolic</code>"
 
option, as that prevents the resolution described above.</li>
 
 
 
<li>If you use <code>dlopen</code> to explicitly load code from a shared
 
library, you must do several things. First, export global symbols from
 
the executable by linking it with the "<code>-E</code>" flag (you will
 
have to specify this as "<code>-Wl,-E</code>" if you are invoking
 
the linker in the usual manner from the compiler driver, <code>g++</code>).
 
You must also make the external symbols in the loaded library
 
available for subsequent libraries by providing the <code>RTLD_GLOBAL</code>
 
flag to <code>dlopen</code>.  The symbol resolution can be immediate or
 
lazy.</li>
 
 
 
</ul>
 
 
 
<p>Template instantiations are another, user visible, case of objects
 
with vague linkage, which needs similar resolution. If you do not take
 
the above precautions, you may discover that a template instantiation
 
with the same argument list, but instantiated in multiple translation
 
units, has several addresses, depending in which translation unit the
 
address is taken. (This is <em>not</em> an exhaustive list of the kind
 
of objects which have vague linkage and are expected to be resolved
 
during linking &amp; loading.)</p>
 
 
 
<p>If you are worried about different objects with the same name
 
colliding during the linking or loading process, then you should use
 
namespaces to disambiguate them. Giving distinct objects with global
 
linkage the same name is a violation of the One Definition Rule (ODR)
 
[basic.def.odr].</p>
 
 
 
<p>For more details about the way that GCC implements these and other
 
C++ features, please read the <a
 
href="http://www.codesourcery.com/cxx-abi/">ABI specification</a>.
 
Note the <code>std::type_info</code> objects which <i>must</i> be
 
resolved all begin with "_ZTS". Refer to <code>ld</code>'s
 
documentation for a description of the "<code>-E</code>" &amp;
 
"<code>-Bsymbolic</code>" flags.</p>
 
 
 
<hr />
 
<h2><a name="generated_files">Why do I need autoconf, bison, xgettext, automake, etc?</a></h2>
 
 
 
<p>If you're using diffs up dated from one snapshot to the next, or
 
if you're using the SVN repository, you may need several additional programs
 
to build GCC.</p>
 
 
 
<p>These include, but are not necessarily limited to autoconf, automake,
 
bison, and xgettext.</p>
 
 
 
<p>This is necessary because neither diff nor cvs keep timestamps
 
correct.  This causes problems for generated files as "make" may think
 
those generated files are out of date and try to regenerate them.</p>
 
 
 
<p>An easy way to work around this problem is to use the <code>gcc_update
 
</code> script in the contrib subdirectory of GCC, which handles this
 
transparently without requiring installation of any additional tools.</p>
 
 
 
 
 
<p>When building from diffs or SVN or if you modified some sources,
 
you may also need to obtain development versions of some GNU tools, as
 
the production versions do not necessarily handle all features needed
 
to rebuild GCC.</p>
 
 
 
<p>In general, the current versions of these tools from <a
 
href="ftp://ftp.gnu.org/gnu/">ftp://ftp.gnu.org/gnu/</a> will work.
 
At present, Autoconf 2.50 is not supported, and you will need to use
 
Autoconf 2.13; work is in progress to fix this problem.  Also look at
 
<a href="ftp://gcc.gnu.org/pub/gcc/infrastructure/">
 
ftp://gcc.gnu.org/pub/gcc/infrastructure/</a> for any special versions
 
of packages.</p>
 
 
 
 
 
<hr />
 
<h2><a name="picflag-needed">Why can't I build a shared library?</a></h2>
 
 
 
<p>When building a shared library you may get an error message from the
 
linker like `assert pure-text failed:' or `DP relative code in file'.</p>
 
 
 
<p>This kind of error occurs when you've failed to provide proper flags
 
to gcc when linking the shared library. </p>
 
 
 
<p>You can get this error even if all the .o files for the shared library were
 
compiled with the proper PIC option.  When building a shared library, gcc will
 
compile additional code to be included in the library.  That additional code
 
must also be compiled with the proper PIC option.</p>
 
 
 
<p>Adding the proper PIC option (<tt>-fpic</tt> or <tt>-fPIC</tt>) to the link
 
line which creates the shared library will fix this problem on targets that
 
support PIC in this manner.  For example:</p>
 
<pre>
 
        gcc -c -fPIC myfile.c
 
        gcc -shared -o libmyfile.so -fPIC myfile.o
 
</pre>
 
 
 
 
 
<hr />
 
<h2><a name="vtables">When building C++, the linker says my constructors, destructors or virtual tables are undefined, but I defined them</a></h2>
 
 
 
<p>The ISO C++ Standard specifies that all virtual methods of a class
 
that are not pure-virtual must be defined, but does not require any
 
diagnostic for violations of this rule [class.virtual]/8.  Based on
 
this assumption, GCC will only emit the implicitly defined
 
constructors, the assignment operator, the destructor and the virtual
 
table of a class in the translation unit that defines its first such
 
non-inline method.</p>
 
 
 
<p>Therefore, if you fail to define this particular method, the linker
 
may complain about the lack of definitions for apparently unrelated
 
symbols.  Unfortunately, in order to improve this error message, it
 
might be necessary to change the linker, and this can't always be
 
done.</p>
 
 
 
<p>The solution is to ensure that all virtual methods that are not
 
pure are defined.  Note that a destructor must be defined even if it
 
is declared pure-virtual [class.dtor]/7.</p>
 
 
 
 
 
</body>
 
</html>
 
 
 No newline at end of file
 No newline at end of file

powered by: WebSVN 2.1.0

© copyright 1999-2024 OpenCores.org, equivalent to Oliscience, all rights reserved. OpenCores®, registered trademark.