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wxWindows Programmer Style Guide
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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_newlogicalops">Don't use new logical operators keywords</A></LI>
+ </OL>
+ <BR>
+ <LI>Other compiler limitations</LI>
+ <OL>
<LI><A HREF="#no_ternarywithobjects">Use ternary operator ?: carefully</A></LI>
+ <LI><A HREF="#no_autoaggregate">Don't use initializers with automatic arrays</A></LI>
+ <LI><A HREF="#no_dtorswithoutctor">Always have at least one constructor in a class with destructor</A></LI>
</OL>
<BR>
<LI>General recommendations</LI>
<OL>
+ <LI><A HREF="#no_cppcommentsinc">No C++ comments in C code></A></LI>
<LI><A HREF="#no_globals">No global variables with constructor</A></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><A HREF="#no_carriagereturn">Avoid carriage returns in cross-platform code</A></LI>
<LI><A HREF="#no_caps_in_filenames">Use only lower letter filenames</A></LI>
<LI><A HREF="#no_incomplete_files">Terminate the files with a new-line</A></LI>
+ <LI><A HREF="#no_case_only_diff">Avoid globals differing by case only</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>
<LI>More about naming conventions</LI>
<OL>
<LI><A HREF="#wx_prefix">Use wx or WX prefix for all public symbols</A></LI>
- <LI><A HREF="#wxdllexport">Use WXDLLEXPORT with all classes/functions in
- wxMSW/common code</A></LI>
+ <LI><A HREF="#wxdllexport">Use WXDLLEXPORT with all classes/functions in wxMSW/common code</A></LI>
<LI><A HREF="#set_get">Use Set/Get prefixes for accessors</A></LI>
<LI><A HREF="#constants">wxNAMING_CONSTANTS</A></LI>
</OL>
years ago, however many compilers still will complain about second declaration
of <TT>i</TT> in the following code:
<PRE>
- for ( int i = 0; i < 10; i++ ) {
+ for ( int i = 0; i < 10; i++ ) {
...
}
...
- for ( int i = 0; i < 10; i++ ) {
+ for ( int i = 0; i < 10; i++ ) {
...
}
</PRE>
-Even if it's perfectly legal now.
+even though if it's perfectly legal now.
<P><U>Workaround</U>: write this instead:
<PRE>
int i;
- for ( i = 0; i < 10; i++ ) {
+ for ( i = 0; i < 10; i++ ) {
...
}
...
- for ( i = 0; i < 10; i++ ) {
+ for ( i = 0; i < 10; i++ ) {
...
}
</PRE>
+or, even better, use different names for the variables in the different for
+loops (in particular, avoid mute variable names like <tt>i<tt> above) - then
+you can declare them in the loop statement and don't pollute the outer name
+space with local loop variables.
<P><LI><A NAME="no_nestedclasses"></A><B>Don't use nested classes</B></LI><P>
Nested classes are, without doubt, a very good thing because they allow to hide
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_newlogicalops"></A><B>Don't use new logical operators keywords</B></LI><P>
+The C++ standard has introduced the following new reserved words: <tt>or</tt>,
+<tt>and</tt>, <tt>not</tt>, <tt>xor</tt>, <tt>bitand</tt>, <tt>bitor</tt>,
+<tt>compl</tt>, <tt>and_eq</tt>, <tt>or_eq</tt>, <tt>not_eq</tt>,
+<tt>or_eq</tt> which can be used instead of the usual C operations &&,
+||, ~ etc.
+<P>This wonderful (and not backwards compatible in addition to being
+absolutely useless) new feature means that these new keywords should not be
+used as the variable names - even if current compilers usually will accept
+this, your code will break in the future. For most of the keywords, using them
+as variable names is quite unlikely, but <tt>or</tt> and <tt>compl</tt> were
+used in the wxWindows sources which seems to indicate that they are the most
+likely candidates.
+<P>It goes without saying that these new keywords should not be used instead
+of the tradional C operators neither both because most compilers don't accept
+them and because using them in C code makes it less readable.
+</OL>
+
+ <BR>
+ <LI>Other compiler limitations</LI><P>
+This section lists the less obvious limitations of the current C++ compilers
+which are less restrictive than the ones mentioned in the previous section but
+are may be even more dangerous as a program which compiles perfectly well on
+some platform and seems to use only standard C++ featurs may still fail to
+compile on another platform and/or with another compiler.
+
+<OL>
<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
+of its operands are objects) because some compilers (notably 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;
+ wxString s = s1.Len() < s2.Len() ? s1 : s2;
// but any C++ compiler will compile this
wxString s;
- if ( s1.Len() < s2.Len() )
+ if ( s1.Len() < s2.Len() )
s = s1;
else
s = s2;
</PRE>
+
+ <P><LI><A NAME="no_autoaggregate"></A><B>Don't use initializers with automatic arrays</B></LI><P>
+The initializers for automatic array variables are not supported by some older
+compilers. For example, the following line
+<PRE>
+ int daysInMonth[12] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
+</PRE>
+will fail to compile with HP-UX C++ compiler.
+<P><U>Workaround</U>: either make the array static or initialize each item
+separately: in the (stupid) example above, the array should be definitely
+declared as <TT>static const</TT> (assuming that the leap years are dealt with
+elsewhere somehow...) which is ok. When an array is really not const, you
+should initialize each element separately.
+
+ <P><LI><A NAME="no_dtorswithoutctor"></A><B>Always have at least one constructor in a class with destructor</B></LI><P>
+It is a good rule to follow in general, but some compilers (HP-UX) enforce it.
+So even if you are sure that the default constructor for your class is ok but
+it has a destructor, remember to add an empty default constructor to it.
</OL>
<BR>
- <LI>General recommendations</
B></LI><P>
+ <LI>General recommendations</LI><P>
While the recommendations in the previous section may not apply to you if you're
only working with perfect compilers which implement the very newest directives of
C++ standard, this section contains compiler- (and language-) independent advice
also contains some C/C++ specific remarks in the end which are less
important.
<OL>
+ <P><LI><A NAME="no_cppcommentsinc"><B>No C++ comments in C code></B></LI><P>
+Never use C++ comments in C code - not all C compilers/preprocessors
+understand them. Although we're mainly concerned with C++ here, there are
+several files in wxWindows sources tree which are compiled with C compiler.
+Among them are <TT>include/wx/setup.h</TT> and <TT>include/wx/expr.h</TT>.
+
+Another thing related to C vs C++ preprocessor differences is that some old C
+preprocessors require that all directives start in the first column (while
+it's generally allowed to have any amount of whitespace before them in C++),
+so you should start them in the beginning of the line in files which are
+compiled with C compiler.
+
<P><LI><A NAME="no_globals"></A><B>No global variables with constructors</B></LI><P>
In C++, the constructors of global variables are called before the
<TT>main()</TT> function (or <TT>WinMain()</TT> or any other program entry point)
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>
</OL>
<BR>
- <LI>Unix/DOS differences</
B></LI><P>
+ <LI>Unix/DOS differences</LI><P>
Two operating systems supported by wxWindows right now are (different flavours
of) Unix and Windows 3.1/95/NT (although Mac, OS/2 and other ports exist/are
being developed as well). The main differences between them are summarized
like files without terminating new-line. Such files also give a warning message
when loaded to vim (the Unix programmer's editor of choice :-)), so please think
about terminating the last line.
+
+ <P><LI><A NAME="no_case_only_diff"></A><B>Avoid globals differing by case only</B></LI><P>
+The linker on VMS is case-insensitive. Therefore all external variables and
+functions which differ only in case are not recognized by the linker as
+different, so all externals should differ in more than the case only:
+i.e. <TT>GetId</TT> is the same as <TT>GetID</TT>.
+
</OL>
<BR>
- <LI>Style choices</
B></LI><P>
+ <LI>Style choices</LI><P>
All wxWindows specific style guidelines are specified in the next
section, here are the choices which are not completely arbitrary,
but have some deeper and not wxWindows-specific meaning.
<OL>
<P><LI><A NAME="naming_conv"></A><B>Naming conventions: use <TT>m_</TT> for members</B></LI><P>
-It's extremely important to write readable code. One of the first steps in this
-direction is the choice of naming convention. It may be quite vague or strictly
-define the names of all the variables and function in the program, however it
-surely must somehow allow the reader to distinguish between variable and
-functions and local variables and member variables from the first glance.
+We all know how important it is to write readable code. One of the first steps
+in this direction is the choice of naming convention. It may be quite vague or
+strictly define the names of all the variables and function in the program,
+however it surely must somehow allow the reader to distinguish between
+variable and functions and local variables and member variables from the first
+glance.
<P>The first requirement is commonly respected, but for some strange reasons, the
second isn't, even if it's much more important because, after all, the immediate
context usually allows you to distinguish a variable from a function in
setup as well to allow including <TT><wx/foo.h></TT> on any platform.<P>
Note that wxWindows implementation files should use quotes when including wxWindows
-headers, not angled brackets. Applications should use angled brackets. There
-is a reason for it (can anyone remember what this is?).
+headers, not angled brackets. Applications should use angled brackets. This
+ensures that the dependencies are correctly handled by the compiler.
<P><LI><A NAME="include_guards"></LI><B>Include guards</B><P>
To minimize the compile time C++ programmers often use so called include
The reason for the strange syntax for data is that some compilers use different
keyword ordering for exporting data.
-<P>There also several other places where you should take care of shared
-library case: all IMPLEMENT_xxx macros which are usually used in the
-corresponding .cpp files must be taken inside
-"<TT>#if !USE_SHARED_LIBRARY</TT>" and in the <TT>#if USE_SHARED_LIBRARY</TT>
-case you should put them inside <TT>common/cmndata.cpp</TT> file.
-
<P><LI><A NAME="set_get"></LI><B>Use Set/Get prefixes for accessors</B><P>
There is a convention in wxWindows to prefix the accessors (i.e. any simple, in
general, inline function which does nothing else except changing or returning
projects / wxWidgets.git / blobdiff