|
|
Hello there,
is it possible to instantiate a std::vector with an incomplete type? E.g.
--Header--
struct field_t;
class all_t
{
...
private:
std::vector<field_t> m_fields;
};
--Implementation--
struct field_t
{
long val1;
int val2;
};
all_t::all_t()
{
...
m_fields.resize(10);
...
}
--End--
What size is assumed by the vector when resize(10) is called? It seems to work with VC7.1 but is it portable or will it overwrite the heap sometimes later?
Regards
Josef
|
|
|
|
|
Josef Schroettle wrote:
is it possible to instantiate a std::vector with an incomplete type? E.g.
Oddly, enough, yes. As long as field_t is known at the time of instantiating variables of type all_t. It seems that any type which embeds a template instantiation doesn't really get instantiated until it's used to declare a value variable (i.e., not a pointer or reference). To be honest, I'm not sure if this is stipulated by the C++ standard or if this is a Microsoft extension.
Josef Schroettle wrote:
or will it overwrite the heap sometimes later?
I doubt it. MSVC doesn't allow you to instantiate all_t unless field_t is known at the point of instantiation. Since field_t is known, then also its size is known, and therefore the heap will be just fine.
If you do find whether this is standard C++ or not, please let me know.
--
Din mamma.
|
|
|
|
|
<small><b>Jörgen Sigvardsson wrote:</b></small>
<i>I doubt it. MSVC doesn't allow you to instantiate all_t unless field_t is known at the point of instantiation. Since field_t is known, then also its size is known, and therefore the heap will be just fine</i>
The question is there, that clients which just include the header file don't know the size of 'T'. But I assume that the vector<T> has always the same size and sizeof(T) is just needed when vector<t> gets memory for a chunk of T's. But in my opinion this is highly depending on the STL implementation, one could e.g. cache the sizeof(T) in a local variable of vector<> which would then be not the real size which is only known to the implementation file.
I'll try asking Scott Meyers which wrote the excellent book 'Effective STL'.
Josef
|
|
|
|
|
Josef Schroettle wrote:
that clients which just include the header file don't know the size of 'T'.
it doesn't matter, because the compiler will not try to calculate the sizes of container<T> until it really has to. Like in a .cpp file. And when that happens, the compiler will remind you that T is unknown if the declaration of T is not visible in the scope you're instantiating container<T>.
--
Din mamma.
|
|
|
|
|
Hello Jörgen,
Scott Meyers answered very fast and I include his reponse below:
-- Scott Meyers wrote ---
Not in portable code. Section 17.4.3.6 of the Standard states that using an incomplete type to instantiate a library component (such as vector) yields undefined behavior. On this topic, I encourage you to read
http://www.cuj.com/documents/s=7986/cujcexp2002austern/
-- End Scott Meyers ---
Sometimes it's good to get an authoritative answer from an expert...
Josef
|
|
|
|
|
Josef Schroettle wrote:
On this topic, I encourage you to read
http://www.cuj.com/documents/s=7986/cujcexp2002austern/
Clickety[^]
|
|
|
|
|
Hello All,
I have a window that runs in a seperate thread, so I have been making a modal dialog box. It only has one item in it, a static control with a picture. I need to make it so you can size down the dialog box and have scroll bars appear. I have done some work where I use scroll bars with a regular CWindowImpl<>, but I don't know how to make that go modal. The easiest way seems to have scroll bars in my dialog box, and it seems that would be an easy thing to do without manually handling all the scrolling logic and moving things around, but heck if I can figure out how to do any of it. 
Also, how can I limit the resizing, like not letting the client area go larger than my picture? It would be REALLY cool to have the maximize button size the client area to the picture. 
All Help is Greatly Appreciated 
-- Rick
|
|
|
|
|
Hello.
I've just written a relatively simple COM application : an ATL COM Server (EXE) providing one COM object. I choosed EXE because I want an existing application (a Win32 server) to have a COM entry point.
First test :
I make a .VBS file that simply instantiate the component and call a method. It works very well. I can even add debug points on the running EXE server to trace the request.
Second test :
In fact, the client is more complicated, it's a DLL (it's an ISAPI extension, built with ATL Server Web Service wizard).
When the client make the SOAP request, the DLL correctly process it, forward it to the EXE COM Server. It looks like it's working correctly but I can't add debug points in my EXE server. After some investigation, it showed that the DLL was not forwarding the request to the running EXE server, it was instantiating another server process ! (as if it was an in process server).
I've got the idea it could be because the ISAPI DLL was running on an account (the IIS one) and the server on another (the current user, me). But after configuring the Web application so it uses my account I still have the same problem : in task manager I can see 2 server process with the same user name.
I'm not a COM Guru, so going short on ideas, anyone know what is happening?
|
|
|
|
|
What happens if you launch two copies of your script simultaneously?
If you still get two copies of your EXE, you probably registered your class objects as REGCLS_SINGLEUSE. This causes the class object's registration to be removed after the first class object was created. Unless you called CoRegisterClassObject again, the next time a call to CoGetClassFactory (which is called internally by CoCreateInstance) occurs, the COM Service Control Manager starts up a new instance of your server.
If you want all clients to use the same server process, you should register your class objects as REGCLS_MULTIPLEUSE.
In an ATL server, you typically register your class objects by calling _Module.RegisterClassObjects in WinMain.
Stability. What an interesting concept. -- Chris Maunder
|
|
|
|
|
When I run multiple clients (script, C++ client, remote client using CoCreateInstanceEx) it works very well, always using the current server instance (yes, using the REGCLS_MULTIPLEUSE, I've trace the ATL code).
But within my ISAPI extension (running in IIS, but with the same account as my COM server) it create another instance of the server (running on the same account) and then all the request use the newly created instance (I never have more than 2 instances).
|
|
|
|
|
Iam currently trying to use URLDownload to file and the prototype for this method is as follows
HRESULT URLDownloadToFile(LPUNKNOWN pCaller,
LPCTSTR szURL,
LPCTSTR szFileName,
DWORD dwReserved,
LPBINDSTATUSCALLBACK lpfnCB
);
The first parameter "LPUNKOWN pCaller" is supposed to be a pointer to the Iunknown interface of my activeX control. But i have very little idea how to obtain this pointer. Would it be possible to either use "Iunknown::addRef" or use "CWnd::GetControlUnknown" to do this? My control is ATL based which as I understand implements the Iunknown interface for me. I am an activeX newbie so..........Any one have any ideas?
[] /\ () X
|
|
|
|
|
It is only required if you want ot have notifications about the progress of download process, if you just want to download a file without any progress bars use this
HRESULT hr = URLDownloadToFile(NULL,"http://...",szFilename,255,NULL);
if(FAILED(hr))
{
MessageBox(NULL,szFilename,"FAILED",MB_OK);
}
Hope it Helps 
C makes it easy to shoot yourself in the foot; C++ makes it harder, but when you do, it blows away your whole leg
|
|
|
|
|
URLDownloadToFile(NULL,"http://...",szFilename, BINDF_GETNEWESTVERSION, NULL);
greatest thing is to do wot others think you cant
suhredayan@omniquad.com>
messenger :suhredayan@hotmail.com
|
|
|
|
|
Hey thanx for the help guys got it working now , till next time.............
[] /\ () X
|
|
|
|
|
Hello everyone:
Is there some WTL structure like POSITION of MFC?
Thank you.
-Freehawk
|
|
|
|
|
No.
I suspect you want the collection classes, use STL instead.
/Magnus
- I don't necessarily agree with everything I say
|
|
|
|
|
Thank you for the reply.
Please tell me How to use STL instead to it?
-Freehawk
|
|
|
|
|
To do what?
/Magnus
- I don't necessarily agree with everything I say
|
|
|
|
|
ATL also has their own array classes that produce smaller object code that STL but aren't as near as powerful.
Pick up a good book on STL. It is really some nice stuff. I personally use the collection classes. Some of the other stuff can be problematic.
Tim Smith
I'm going to patent thought. I have yet to see any prior art.
|
|
|
|
|
It's a steep learning curve if u don't even have MFC Background.
To start with ATL suggested by Tim, u got to know where to get the documentation from.
Look into \vc98\ATL\ATLwin.h for example. U get all the ATL helper classes.
STL is purely for C++ gurus only, ATL is a build up from STL. U need to know ur STL before u know what's happening in ATL. ATL is sort of superceded by WTL now. So look up WTL for better wrapper classes which are equivalents of those classes in MFC.
|
|
|
|
|
Try this link, should be helpful for u to know what new template classes are out there for u to use.
http://www.viksoe.dk/wtldoc/
|
|
|
|
|
Anonymous wrote:
It's a steep learning curve if u don't even have MFC Background.
We can assume that freehawk already has an MFC background since he refers to POSITION.
Anonymous wrote:
STL is purely for C++ gurus only
No, it's not. I'm nowhere near being a C++ guru and use STL comfortably. In any case, it is now part of Standard C++ and anyone wanting to be a professional programmer needs to know how to use it. You do not need to understand everything about it to benefit from it. Just start slowly...
Kevin
|
|
|
|
|
There are plenty of articles here at CodeProject.
You might also try looking at the numerous examples in the VC online help. That's how I got going initially with basic use of strings, vectors, lists and so on.
There's also quite a good online tutorial here. http://www.sgi.com/tech/stl/[^]
Kevin
|
|
|
|
|
General 
News 
Suggestion 
Question 
Bug 
Answer 
Joke 
Praise 
Rant 
Admin 
Submit an article or tip
