Re: What is going on here?
JoeC wrote:
Kai-Uwe Bux wrote:
JoeC wrote:
Ian Collins wrote:
JoeC wrote:
I have been programming for a while and I have seen this syntax before
and I copied this from a book but the book didn't explain what is
going on here.
class engine{
protected:
static engine* pengine;
What an unfortunate name, reads like penguin!
Than later:
if(initialize(hin)){
if(!engine::gengine()->init(CmdShow)){return false;}
This would be a syntax error, you have declared "pengine" as a pointer
and here you are attempting to invoke operation () on it.
while(TRUE){
[snip]
At first sight, I was thinking that you may have come across the
singleton pattern. However, I cannot confirm that from the more code you
posted. Please note that the most important parts would be the places
where pengine is set, where the pointee of pengine is created, and where
it is destroyed (if at all). If you post those parts, it may become
aparent what is going on. So far, we have to assume that pengine==NULL,
which seems a little unlikely.
[snip]
This code is from Game Programming in 24 Hours by Michael Morrison. I
copied the code shortening some of the words. I did use this code and
his basic engine for a few projects. I didn't like the engine too much
because I didn't understand it well and decided not to create a windows
object for my later projects. I have limited experience in programming
and it is hard for me to tell good code from bad especially in larger
programs.
This was a construct that I have not seen in any other book so I asked
about it.
As I said above: first, I thought you may have encountered the singleton
pattern. However, the code you posted subsequently did neither confirm nor
refute that hypothesis since it did not contain the parts where pengine is
set (apart from some 0-initialization).
Assuming that it was meant to be a singleton, I would have expected code
like this:
class Singleton {
public:
static Singleton* Instance() {
static Singleton* result = new Singleton;
return ( result );
}
protected:
Singleton() {}
Singleton(const Singleton&);
Singleton& operator= (const Singleton&);
};
The point of a singleton is that there shall be one and only one instance of
a class, created upon first use and uniformly accessible throughout the
program. I do not know of any convincing examples as to when a singleton
pattern is actually a good idea; usually I do not see a logical necessity
for the class to prevent multiple instantiation and it suffices entirely to
only create a single object if you don't need several (keep it simple!).
Even though (or because) the singleton is possibly the most frequently
misused pattern, it is very important and you definitely should read about
it if you don't know it already.
I have written some fairly large programs that run well.
Because I work in isolation, I have limited influences of other
programmers.
This news group surely helps me a lot to cross check my ideas.
If this is bad code thanks for the help. It complied and rand and it
allowed me to animate some graphics around the screen.
I did not mean to insult you or to denigrate your work. I merely felt the
need to point out that the code has some serious shortcomings and should
not be used as a guideline for programming. The most devastating criticism,
however, came from yourself when you said:
I didn't like the engine too much because I didn't understand it well
Seems like it wasn't written well enough to be understood well.
As for the construct you found, maybe you can find where in the code the
variable pengine is set to a non-zero value. If so, you may be able to tell
whether we have a singleton before us, or not.
Best
Kai-Uwe Bux