by <A HREF=mailto:zeitlin@dptmaths.ens-cachan.fr>Vadim Zeitlin</A><P>
This guide is intended for people who are (or intending to start) writing code
-for <A HREF="http://web.ukonline.co.uk/julian.smart/wxwin/" target=_top>wxWindows</A> class library.
+for <A HREF="http://www.wxwindows.org" target=_top>wxWindows</A> class library.
<P>
The guide is separated into two parts: the first one addresses the general
many restrictions on the programmer.
<P>
Acknowledgements: This guide is partly based on <A
-HREF=http://www.mozilla.org/docs/tplist/catBuild/portable-cpp.html target=_top>
+HREF="http://www.mozilla.org/hacking/portable-cpp.html" target=_top>
C++ portability guide</A> by David Williams.
<P>
<LI><A HREF="#no_stl">Don't use STL</A></LI>
<LI><A HREF="#no_fordecl">Don't declare variables inside <TT>for()</TT></A></LI>
<LI><A HREF="#no_nestedclasses">Don't use nested classes</A></LI>
+ <LI><A HREF="#no_ternarywithobjects">Use ternary operator ?: carefully</A></LI>
</OL>
<BR>
<LI>General recommendations</LI>
<LI><A HREF="#no_warnings">Turn on all warnings and eradicate them</A></LI>
<LI><A HREF="#no_assume_sizeof">Don't rely on <TT>sizeof(int) == 2</TT>...</A></LI>
<LI><A HREF="#no_assignment_in_if">No assignments in conditional expressions</A></LI>
- <LI><A HREF="#no_comment_code">Use <TT>#if 0</TT> rather than comments to temporarily
- disable blocks of code</A></LI>
+ <LI><A HREF="#no_comment_code">Use <TT>#if 0</TT> rather than comments to temporarily disable blocks of code</A></LI>
+ <LI><A HREF="#no_overloaded_virtuals">Avoid overloaded virtual functions</A></LI>
<LI><A HREF="#no_extra_semicolon">Don't use extra semi-colons on top level</A></LI>
</OL>
<BR>
<LI>Style choices</LI>
<OL>
<LI><A HREF="#naming_conv">Naming conventions: use <TT>m_</TT> for members</A></LI>
- <LI><A HREF="#no_void_param">Don't use <TT>void</TT> for functions without
- arguments</A></LI>
- <LI><A HREF="#no_const_int">Don't use <TT>const</TT> for non pointer/reference
- arguments</A></LI>
+ <LI><A HREF="#no_void_param">Don't use <TT>void</TT> for functions without arguments</A></LI>
+ <LI><A HREF="#no_const_int">Don't use <TT>const</TT> for non pointer/reference arguments</A></LI>
</OL>
</UL>
<P>A nice side effect is that you don't need to recompile all the files
including the header if you change the PrivateLibClass declaration (it's
an example of a more general interface/implementation separation idea).
+
+ <P><LI><A NAME="no_ternarywithobjects"></A><B>Use ternary operator ?: carefully</B></LI><P>
+ The ternary operator <TT>?:</TT> shouldn't be used with objects (i.e. if any
+of its operands are objects) because some compilers (notable Borland C++) fail
+to compile such code.
+<P><U>Workaround</U>: use <TT>if/else</TT> instead.
+<PRE>
+ wxString s1, s2;
+
+ // Borland C++ won't compile the line below
+ wxString s = s1.Len() < s2.Len() ? s1 : s2;
+
+ // but any C++ compiler will compile this
+ wxString s;
+ if ( s1.Len() < s2.Len() )
+ s = s1;
+ else
+ s = s2;
+</PRE>
</OL>
<BR>
The reason is simple: if there are any <TT>/* ... */</TT> comments inside
<TT>...</TT> the second version will, of course, miserably fail.
+ <P><LI><A NAME="no_overloaded_virtuals"></A><B>Avoid overloaded virtual functions</B></LI><P>
+
+You should avoid having overloaded virtual methods in a base class because if
+any of them is overriden in a derived class, then all others must be overriden
+as well or it would be impossible to call them on an object of derived class.
+
+For example, the following code:
+
+<PRE>
+ class Base
+ {
+ public:
+ virtual void Read(wxFile& file);
+ virtual void Read(const wxString& filename);
+ };
+
+ class Derived : public Base
+ {
+ public:
+ virtual void Read(wxFile& file) { ... }
+ };
+
+ ...
+
+ Derived d;
+ d.Read("some_filename"); // compile error here!
+</PRE>
+
+will fail to compile because the base class function taking <TT>filename</TT>
+is hidden by the virtual function overriden in the derived class (this is
+known as [virtual] function name hiding problem in C++).
+
+<P>
+The standard solution to this problem in wxWindows (where we have such
+situations quite often) is to make both <TT>Read()</TT> functions not virtual
+and introduce a single virtual function <TT>DoRead()</TT>. Usually, it makes
+sense because the function taking a filename is (again, usually) implemented
+in terms of the function reading from a file anyhow (but making only this
+functions not virtual won't solve the above problem!).
+<P>
+So, the above declarations should be written as:
+<PRE>
+ class Base
+ {
+ public:
+ void Read(wxFile& file);
+ void Read(const wxString& filename);
+
+ protected:
+ virtual void DoRead(wxFile& file);
+ };
+
+ class Derived : public Base
+ {
+ protected:
+ virtual void DoRead(wxFile& file) { ... }
+ };
+</PRE>
+
+This technique is widely used in many of wxWindows classes - for example,
+<TT>wxWindow</TT> has more than a dozen of <TT>DoXXX()</TT> functions which
+allows to have many overloaded versions of commonly used methods such as
+<TT>SetSize()</TT>
+
<P><LI><A NAME="no_extra_semicolon"></A><B>Don't use extra semi-colons on top level</B></LI><P>
Some compilers don't pay any attention to extra semicolons on top level, as in
<PRE>
projects / wxWidgets.git / blobdiff