}
}
Static constructors don't work reliably either. A static initialized object is an object which is instanciated at
startup time (just before main() is called). Usually there are two components to these objects. First there is
the data segment which is static data loaded into the global data segment of the program. The second part is a
initializer function that is called by the loader before main() is called. We've found that many compilers do
not reliably implement the initializer function. So you get the object data, but it is never initialized. One
workaround for this limitation is to write a wrapper function that creates a single instance of an object, and
replace all references to the static initialized object with a call to the wrapper function:
Portable example:
static FooBarClass* static_object;
FooBarClass*
getStaticObject()
{
if (!static_object)
static_object =
new FooBarClass(87, 92);
return static_object;
}
void
bar()
{
if (getStaticObject()->count > 15) {
...
}
}
Don't use exceptions.
Exceptions are another C++ feature which is not very widely implemented, and as such, their use is not
portable C++ code. Don't use them. Unfortunately, there is no good workaround that produces similar
functionality.
One exception to this rule (don't say it) is that it's probably ok, and may be necessary to use exceptions in
some machine specific code. If you do use exceptions in machine specific code you must catch all exceptions
there because you can't throw the exception across XP (cross platform) code.
3.
Don't use Run-time Type Information.
Run-time type information (RTTI) is a relatively new C++ feature, and not supported in many compilers.
Don't use it.
If you need runtime typing, you can achieve a similar result by adding a classOf() virtual member function
to the base class of your hierarchy and overriding that member function in each subclass. If classOf()
returns a unique value for each class in the hierarchy, you'll be able to do type comparisons at runtime.
4.
Don't use namespace facility.
Support of namespaces (through the namespace and using keywords) is a relatively new C++ feature, and
not supported in many compilers. Don't use it.
5.
main() must be in a C++ file.
The first C++ compiler, Cfront, was in fact a very fancy preprocessor for a C compiler. Cfront reads the C++
code, and generates C code that would do the same thing. C++ startup is slightly different to C startup (for
example static constructor functions must be called for C++), and Cfront implements this special startup by
noticing the function called "main()", converting it to something else (like "__cpp__main()"), adding
another main() that does the special C++ startup things and then calls the original function. Of course for all
this to work, Cfront needs to see the main() function, hence main() must be in a C++ file. Most compilers
lifted this restriction years ago, and deal with the C++ special initialization duties as a linker issue. But there
are a few commercial compilers shipping that are still based on Cfront: HP, and SCO, are examples.
6.
C++ portability guide
http://www.cs.umd.edu/users/cml/cstyle/mozilla-portable-cpp.html (3 of 15) [10/1/2000 7:42:12 PM]
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