PHWinfo - Afficher un message - How to create static array of template class object?

30/06/2008, 09h24

* flowstudioLA@gmail.com:
> I have a template class object that I use as a mesaging queue between
> threads. I use it as a static object that I initialize like so:
>
> foo.h
> class foo{
> static LFQueue<const char*,100> lfqMyQueue;
> };
> foo.cpp
> LFQueue<const char*,100> Foo::lfqMyQueue;

You're using threads and you're using char* pointers for communication between
them, and packaging things in templates just for added complexity.

That means that it should not be surprising if things don't work.

> This has worked fine for me. The problems that I've run into is when
> I've attempted to get tricky and try and declare a number of LFQueue
> objects in a static array, so that I can access a number of queues out
> of a single object. I tried to do it like so:
>
> foo.h
> class foo{
> static LFQueue<const char*,100> aLFQArray[3];
> };
> foo.cpp
> LFQueue<const char*,100> Foo::aLFQArray[3];

The declarations should work fine.

But possibly you haven't shown all relevant code.

> This compiles ok, but when I use it, the const char data goes out of
> scope

That's meaningless.

> and I get garbage when trying to read from the queue.

Not surprising.

> I'm not
> sure if I failed to set it up right, or if the way the queue template
> class is setup makes this impossible. It's almost like the array is
> static, but the LFQueue elements are not?

It's almost like as if doing threading and mixing in char* and perhaps other raw
pointers, and mixing in some templating, at beginner's level, is a recipe for
disaster?

Yes?

You're concentrating on the wrong things, both wrt. what could cause the
failure, and wrt. learning C++ programming.

> Anyway, if any of you could shed some light on how I could go about
> this given what you see above, that would be great. If you need more
> info I can post the LFQueue Template class code, but I wanted to make
> sure it wasn't something obvious with the way this was being declared.

The declaration seems to be OK.

Try to reduce the problem to a minimum, non-threading program that you can post
in its entirety here (compilable by others).

Cheers, & hth.,

- Alf

--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?

30/06/2008, 09h24	#2
Alf P. Steinbach Messages: n/a Hébergeur:	Re: How to create static array of template class object? * flowstudioLA@gmail.com: > I have a template class object that I use as a mesaging queue between > threads. I use it as a static object that I initialize like so: > > foo.h > class foo{ > static LFQueue<const char,100> lfqMyQueue; > }; > foo.cpp > LFQueue<const char,100> Foo::lfqMyQueue; You're using threads and you're using char* pointers for communication between them, and packaging things in templates just for added complexity. That means that it should not be surprising if things don't work. > This has worked fine for me. The problems that I've run into is when > I've attempted to get tricky and try and declare a number of LFQueue > objects in a static array, so that I can access a number of queues out > of a single object. I tried to do it like so: > > foo.h > class foo{ > static LFQueue<const char,100> aLFQArray[3]; > }; > foo.cpp > LFQueue<const char,100> Foo::aLFQArray[3]; The declarations should work fine. But possibly you haven't shown all relevant code. > This compiles ok, but when I use it, the const char data goes out of > scope That's meaningless. > and I get garbage when trying to read from the queue. Not surprising. > I'm not > sure if I failed to set it up right, or if the way the queue template > class is setup makes this impossible. It's almost like the array is > static, but the LFQueue elements are not? It's almost like as if doing threading and mixing in char* and perhaps other raw pointers, and mixing in some templating, at beginner's level, is a recipe for disaster? Yes? You're concentrating on the wrong things, both wrt. what could cause the failure, and wrt. learning C++ programming. > Anyway, if any of you could shed some light on how I could go about > this given what you see above, that would be great. If you need more > info I can post the LFQueue Template class code, but I wanted to make > sure it wasn't something obvious with the way this was being declared. The declaration seems to be OK. Try to reduce the problem to a minimum, non-threading program that you can post in its entirety here (compilable by others). Cheers, & hth., - Alf -- A: Because it messes up the order in which people normally read text. Q: Why is it such a bad thing? A: Top-posting. Q: What is the most annoying thing on usenet and in e-mail?