<ol>
<li><a href="#scf_commenting">Commenting</a></li>
<li><a href="#scf_commentformat">Comment Formatting</a></li>
- <li><a href="#scf_includes">#include Style</a></li>
+ <li><a href="#scf_includes"><tt>#include</tt> Style</a></li>
<li><a href="#scf_codewidth">Source Code Width</a></li>
<li><a href="#scf_spacestabs">Use Spaces Instead of Tabs</a></li>
<li><a href="#scf_indentation">Indent Code Consistently</a></li>
<li><a href="#micro">The Low Level Issues</a>
<ol>
<li><a href="#hl_assert">Assert Liberally</a></li>
+ <li><a href="#hl_ns_std">Do not use 'using namespace std'</a></li>
<li><a href="#hl_preincrement">Prefer Preincrement</a></li>
- <li><a href="#hl_avoidendl">Avoid std::endl</a></li>
- <li><a href="#hl_exploitcpp">Exploit C++ to its Fullest</a></li>
+ <li><a href="#hl_avoidendl">Avoid <tt>std::endl</tt></a></li>
</ol></li>
</ol></li>
<li><a href="#seealso">See Also</a></li>
<div class="doc_text">
<p>Comments are one critical part of readability and maintainability. Everyone
-knows they should comment, so should you. :) Although we all should probably
+knows they should comment, so should you. Although we all should probably
comment our code more than we do, there are a few very critical places that
documentation is very useful:</p>
a class definition should have a comment block that explains what the class is
used for... if it's not obvious. If it's so completely obvious your grandma
could figure it out, it's probably safe to leave it out. Naming classes
-something sane goes a long ways towards avoiding writing documentation. :)</p>
+something sane goes a long ways towards avoiding writing documentation.</p>
<b>Method information</b>
<ol>
<li>When writing a C code: Obviously if you are writing C code, use C style
- comments. :)</li>
- <li>When writing a header file that may be #included by a C source file.</li>
+ comments.</li>
+ <li>When writing a header file that may be <tt>#include</tt>d by a C source
+ file.</li>
<li>When writing a source file that is used by a tool that only accepts C
style comments.</li>
</ol>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
- <a name="scf_includes">#include Style</a>
+ <a name="scf_includes"><tt>#include</tt> Style</a>
</div>
<div class="doc_text">
<p>... and each catagory should be sorted by name.</p>
<p><a name="mmheader">The "Main Module Header"</a> file applies to .cpp file
-which implement an interface defined by a .h file. This #include should always
-be included <b>first</b> regardless of where it lives on the file system. By
-including a header file first in the .cpp files that implement the interfaces,
-we ensure that the header does not have any hidden dependencies which are not
-explicitly #included in the header, but should be. It is also a form of
-documentation in the .cpp file to indicate where the interfaces it implements
-are defined.</p>
+which implement an interface defined by a .h file. This <tt>#include</tt>
+should always be included <b>first</b> regardless of where it lives on the file
+system. By including a header file first in the .cpp files that implement the
+interfaces, we ensure that the header does not have any hidden dependencies
+which are not explicitly #included in the header, but should be. It is also a
+form of documentation in the .cpp file to indicate where the interfaces it
+implements are defined.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
- <a name="hl_dontinclude">#include as Little as Possible</a>
+ <a name="hl_dontinclude"><tt>#include</tt> as Little as Possible</a>
</div>
<div class="doc_text">
have to, especially in header files.</p>
<p>But wait, sometimes you need to have the definition of a class to use it, or
-to inherit from it. In these cases go ahead and #include that header file. Be
-aware however that there are many cases where you don't need to have the full
-definition of a class. If you are using a pointer or reference to a class, you
-don't need the header file. If you are simply returning a class instance from a
-prototyped function or method, you don't need it. In fact, for most cases, you
-simply don't need the definition of a class... and not <tt>#include</tt>'ing
-speeds up compilation.</p>
+to inherit from it. In these cases go ahead and <tt>#include</tt> that header
+file. Be aware however that there are many cases where you don't need to have
+the full definition of a class. If you are using a pointer or reference to a
+class, you don't need the header file. If you are simply returning a class
+instance from a prototyped function or method, you don't need it. In fact, for
+most cases, you simply don't need the definition of a class... and not
+<tt>#include</tt>'ing speeds up compilation.</p>
<p>It is easy to try to go too overboard on this recommendation, however. You
<b>must</b> include all of the header files that you are using, either directly
<p>Many modules have a complex implementation that causes them to use more than
one implementation (<tt>.cpp</tt>) file. It is often tempting to put the
internal communication interface (helper classes, extra functions, etc) in the
-public module header file. Don't do this. :)</p>
+public module header file. Don't do this.</p>
<p>If you really need to do something like this, put a private header file in
the same directory as the source files, and include it locally. This ensures
</div>
+<!-- _______________________________________________________________________ -->
+<div class="doc_subsubsection">
+ <a name="hl_ns_std">Do not use 'using namespace std'</a>
+</div>
+
+<div class="doc_text">
+<p>In LLVM, we prefer to explicitly prefix all identifiers from the standard
+namespace with an "std::" prefix, rather than rely on "using namespace std;".
+</p>
+
+<p> In header files, adding a 'using namespace XXX' directive pollutes the
+namespace of any source file that includes the header. This is clearly a bad
+thing.</p>
+
+<p>In implementation files (e.g. .cpp files) the rule is more of a stylistic
+rule, but is still important. Basically, using explicit namespace prefixes
+makes
+the code <b>more clear</b> - because it is immediately obvious what facilities
+are being used and where they are coming from - and <b>more portable</b> -
+because namespace clashes cannot occur between LLVM code and other namespaces.
+The portability rule is important because different standard library
+implementations expose different symbols (potentially ones they shouldn't) and
+future revisions to the C++ standard will add more symbols to the std
+namespace. As such, we never 'using namespace std;' in LLVM.</p>
+
+<p>The exception to the general rule (i.e. it's not an exception for the std
+namespace) is for implementation files. For example, all of the code in the
+LLVM project implements code that lives in the 'llvm' namespace. As such, it
+is ok, and actually more clear, for the .cpp files to have a 'using namespace
+llvm' directive at their top, after the #includes. The general form of this
+rule is that any .cpp file that implements code in any namespace may use that
+namespace (and its parents), but should not use any others.</p>
+
+</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
- <a name="hl_avoidendl">Avoid std::endl</a>
+ <a name="hl_avoidendl">Avoid <tt>std::endl</tt></a>
</div>
<div class="doc_text">
</div>
-<!-- _______________________________________________________________________ -->
-<div class="doc_subsubsection">
- <a name="hl_exploitcpp">Exploit C++ to its Fullest</a>
-</div>
-
-<div class="doc_text">
-
-<p>C++ is a powerful language. With a firm grasp on its capabilities, you can
-make write effective, consise, readable and maintainable code all at the same
-time. By staying consistent, you reduce the amount of special cases that need
-to be remembered. Reducing the total number of lines of code you write is a
-good way to avoid documentation, and avoid giving bugs a place to hide.</p>
-
-<p>For these reasons, come to know and love the contents of your local
-<algorithm> header file. Know about <functional> and what it can do
-for you. C++ is just a tool that wants you to master it. :)</p>
-
-</div>
-
<!-- *********************************************************************** -->
<div class="doc_section">
<a name="seealso">See Also</a>
</ol>
<p>If you get some free time, and you haven't read them: do so, you might learn
-something. :)</p>
+something.</p>
</div>
src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
<a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
- <a href="http://llvm.cs.uiuc.edu">LLVM Compiler Infrastructure</a><br>
+ <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br>
Last modified: $Date$
</address>
projects / oota-llvm.git / blobdiff