====== Compiling With Clang ======

===== Introduction =====

This short tutorial describes the details of compiling ''edelib'' and ''EDE'' with the [[http://clang.llvm.org/|Clang]] compiler. It is assumed you
already have installed a Clang version with the needed libraries.

:!: **Note:** This tutorial also assumes you have read InstallationHowTo and have prepared the needed libraries and tools.

===== Compiling FLTK =====

First we are going to compile ''FLTK''. ''Clang'' can use libraries compiled with ''GCC'', so if you can install the latest stable version of ''FLTK'' with your distribution's package management system, feel free to do so.

However, if you prefer to compile ''FLTK'' with ''Clang'' as well, first download ''FLTK'''s source code, unpack it and run the following commands in terminal:

<code>
$ cd fltk-<version>
$ export CC=clang
$ export CXX=clang++
$ ./configure && make
</code>

or in case you would like ''FLTK'' to be installed on different place (default is
///usr/local//, use the //prefix//) parameter, like:

<code>
$ ./configure --prefix=/usr && make
</code>

and as superuser, run:

<code>
$ make install
</code>

===== Compiling edelib =====

Normally ''edelib'' should compile without problems and compilation
commands are pretty much the same as for compiling ''FLTK'' (except you are
using //JAM// as build tool). The commands in the right order are:

<code>
$ cd edelib-<version>
$ export CC=clang
$ export CXX=clang++
$ ./configure && jam
</code>

You can use the //prefix// parameter to set the desired location. As superuser,
running:

<code>
$ jam install
</code>

will install ''edelib'' to the desired location.

===== Compiling EDE =====

The commands to build ''edelib'' apply here, too. However, if you get strange errors like:

<code>
In file included from ActionMenu.cc:14:
In file included from /usr/bin/../lib/gcc/i686-redhat-linux/4.7.2/../../../../include/c++/4.7.2/iostream:39:
In file included from /usr/bin/../lib/gcc/i686-redhat-linux/4.7.2/../../../../include/c++/4.7.2/ostream:39:
In file included from /usr/bin/../lib/gcc/i686-redhat-linux/4.7.2/../../../../include/c++/4.7.2/ios:42:
In file included from /usr/bin/../lib/gcc/i686-redhat-linux/4.7.2/../../../../include/c++/4.7.2/bits/ios_base.h:40:
/usr/bin/../lib/gcc/i686-redhat-linux/4.7.2/../../../../include/c++/4.7.2/ext/atomicity.h:48:45: error: use of undeclared identifier '__ATOMIC_ACQ_REL'
  { return __atomic_fetch_add(__mem, __val, __ATOMIC_ACQ_REL); }
                                            ^
/usr/bin/../lib/gcc/i686-redhat-linux/4.7.2/../../../../include/c++/4.7.2/ext/atomicity.h:52:38: error: use of undeclared identifier '__ATOMIC_ACQ_REL'
  { __atomic_fetch_add(__mem, __val, __ATOMIC_ACQ_REL); }
                                     ^
</code>

you are probably running a recent ''GCC'' version with a ''Clang'' version a bit older. If your distribution does not provide an updated ''Clang'' package,
you can apply a small hack.

:!: **Please note that this hack can change how gcc works, so after you change the given file, recompile ''EDE'' and revert those changes!**

As superuser, open the file ///usr/include/c++/VERSION/PLATFORM-DISTRO/bits/c++config.h//, where //VERSION// is the ''GCC'' version (like 4.7.2) and //PLATFORM-DISTRO// is distribution specific folder, like //i686-redhat-linux//. Find the line:

<code cpp>
#define _GLIBCXX_ATOMIC_BUILTINS 1
</code>

and comment it out, like:

<code cpp>
// #define _GLIBCXX_ATOMIC_BUILTINS 1
</code>

which will disable ''GCC'' builtin atomic access functions. Recompile ''EDE'' and install it, uncommenting above line afterwards.