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Hi,
to truncate a file, you can open it for writing, then close it.
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What no codes? 
led mike
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led mike wrote: no codes?
No C++ codes today. Am still recovering from a little Fortran experience. All upper-case.
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int MapFileSizeToZero(size_t filesize)
{
return 0;
}
If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke
[My articles]
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Damn, you read my mind 
Regards,
--Perspx
"A refund for defective software might be nice, except it would bankrupt the entire software industry in the first year."
-Andrew Tanenbaum
"Einstein argued that there must be simplified explanations of nature, because God is not capricious or arbitrary. No such faith comforts the software engineer."
-Fred Brooks
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BTW: the quotes in your sign are wonderful.
If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke
[My articles]
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CPallini wrote: BTW: the quotes in your sign are wonderful.
Thank you I'm always sure to pluck them carefully from Wikiquote from my plethora of knowledge
Regards,
--Perspx
"A refund for defective software might be nice, except it would bankrupt the entire software industry in the first year."
-Andrew Tanenbaum
"Einstein argued that there must be simplified explanations of nature, because God is not capricious or arbitrary. No such faith comforts the software engineer."
-Fred Brooks
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Hi,
When using overlapped named pipes for Interprocess comunication between a Dos Console Program Acting as The Server and A Windows 32 GUI acting as the Client or Child Process
Do I have Share the hEvent Kernel Object which is part othe Overlapped Structure
Between the Dos Console program (which creates it) and The Windows Program
I would think so ...
Any insight about this issue would be appreciated
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ForNow wrote: Do I have Share the hEvent Kernel Object which is part othe Overlapped Structure
Even if you could share an event across processes, why? What are you going to do with it?
From your post it seems likely you have not yet stabilized your understanding of Overlapped I/O and perhaps IPC in general.
led mike
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The way I understand Overlapped or async . I/O is the following
In the Server or Dos Program (in my case) I do a CreateNamePipe
Create The hEvent via CreateEvent for the hEvent which is part of Overlapped stucture
I then do a Connectnamed pipe waiting for the Client (in My case Windows Program ..started with CreateProcess)
to connect
In the Client (my Windows program) does A CreateFile which effectivly establishes the connection
with FILE_FLAGGED_OVERLAPPED making this a async./overlapped connection
It was my understanding that If my Windows program were to do a WriteFile that hEvent of the Overlapped
structure would be signaled and that is Why I thought it was A KernelObject that had to be shared by the
Client (Dos Console) when doing the ReadFile or Have A WaitForSingleObject withe shared hEvent just before
the ReadFile
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ForNow wrote: making this a async./overlapped connection
It's not the connection that is asynchronous/overlapped....
it's individual I/O operations that can be executed asynchronously/overlapped.
The client end knows nothing about your server's overlapped operations
and vice versa.
When you do an overlapped I/O operation, you're essentially just queuing the operation
for completion asynchronously relative to the thread starting the operation.
When your server does an overlapped ConnectNamedPipe(), the event you pass in
your overlapped struct is used to signal the completion of that operation only, which
is when a client connects with CreateFile() or CallNamedPipe(). The system will
signal the event.
The server then could then call ReadFile() overlapped/asynchronously to read data
from the client, in which case you could use the event to know when the read operation
is complete. Again, the system signals the event.
An overlapped structure holds a context for each operation (and anything else you
want to put in there).
How you manage the overlapped structs and their lifetime is up to you. The system just passes
them around (e.g. you get the same LPOVERLAPPED back in GetOverlappedResult()).
Make sense? There's nothing about any of this requiring an endpoint to have the other
end's event handles or overlapped structs. The client could use synchronous I/O while
the server uses asynchronous I/O, or whatever combination you want.
Mark
Mark Salsbery
Microsoft MVP - Visual C++
![Java | [Coffee]](https://codeproject.global.ssl.fastly.net/script/Forums/Images/coffee.gif)
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Thankx
Do I use the same hEvent from the ConnectNamedPipe for Readfile Writefile ???
Does the Overlapped with hEvent Haver to be In Global Storage I would think it would be a good Idea if Readfile and
Writefile use it it should n't be on the Stack of any routine
Thankx Again
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ForNow wrote: Do I use the same hEvent from the ConnectNamedPipe for Readfile Writefile ???
You can. It depends on how you plan to use the event and how many outstanding
operations you plan on having at any given time.
Typically, you'd use the event if you have an I/O completion thread (or threads)
that waits for the signalled event(s) and processes the completed I/O operation.
In that case, you only need one event per completion-handler thread.
If you're not using completion handler threads then you don't need the event
at all - you can poll for completion with GetOverlappedResult().
Note that with ConnectNamedPipe() you'd probably want/need to use a handler thread -
essentially a "listener" thread listening for incoming client connections.
You need to manage the lifetime of the overlapped structs as well as any event handles you create.
For the event handles, the handle is stored in the OVERLAPPED struct so you only need to
free it when you're no longer using the struct object.
For the OVERLAPPED structures themselves - you may need only one or many depending on
how you're handling your I/O. You can even implement a pre-created pool of them.
FWIW, you can wrap OVERLAPPED structs in any structure you want to, as long as you pass
a pointer to the OVERLAPPED struct to functions that use it. That's handy for keeping
things like allocated I/O buffers with an OVERLAPPED struct.
Example: I have used something similar to this for read/write I/O...
#pragma pack( push, MY_OVERLAPPEDpack, 1 )
struct MY_OVERLAPPED
{
OVERLAPPED Overlapped;
SomeClass *pOwnerObject;
DWORD DataBufferLength;
BYTE *pDataBuffer;
};
#pragma pack( pop, MY_OVERLAPPEDpack)
typedef CTypedPtrList<cptrlist,> MY_OVERLAPPEDPtrList;
Mark Salsbery
Microsoft MVP - Visual C++
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BTW do you work for MicroSoft What Does MicroSoft MVP imply ???
Thanx Again Going to give it a shot
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ForNow wrote: I would think so ...
Why? An endpoint knows NOTHING about the use of overlapped I/O
on the other end.
ForNow wrote: Do I have Share the hEvent Kernel Object which is part othe Overlapped Structure
No 
Mark Salsbery
Microsoft MVP - Visual C++
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Hi all. I'm implementing a macro that I need to have take multiple parameters.
Let's say I'm implementing a printf macro. (I know. I know. Just run with me for the example.  )
#define PRINT(str,...) printf(str,__VAR_ARGS__);
Well, obviously, someone could invoke the macro thusly:
PRINT("My name is %s and I am %i years old.", szName, iAge);
After doing some research, I found __VAR_ARGS__ on gamedev.net. Just one problem: Visual Studio 2008 is not aware for __VAR_ARGS__.
Am I misspelling __VAR_ARGS__ or something?
What header file is __VAR_ARGS__ (or its correctly spelled version!!) defined?
K, thanks!
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varargs.h by any chance? 
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Well, actually, I think I figured it out.
It's: __VA_ARGS__
#define PRINT(str,...) printf(str, __VA_ARGS__); //not __VAR_ARGS__ lose the first 'R'.
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indeed, however vaargs.h won't cut it.
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hehe. Yeah, I'm still searching for where __VA_ARGS__ *is* defined. I wonder if it's hardcoded into the compiler itself. The C99 standard says it should be supported - whether MS supports it or not I'm truly not at liberty to say until I've tested my still compiling application. (~700K lines).
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I searched for varargs.h and only my WinARM and cygwin directories have those files.
Still searching the tree for __VA_ARGS__.
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Hi, my folder C:\Program Files\Microsoft Visual Studio 9.0\VC\include
holds a varargs.h file containing definitions for _VA_LIST, va_start(ap), va_arg(ap,t), and more.
Yes, __VA_ARGS__ seems not to be there, I think you're right the compiler knows all about that one without any include file.
[ADDED]
Their documentation[^] knows about it; and you could test it with a much smaller program...
[/ADDED]
modified on Tuesday, December 9, 2008 1:09 PM
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/hug
See, this is why I love The Code Project!
Thank you, Luc!
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Looking at this page about variadic macros[^], it should be __VA_ARGS__?
You won't find it in any header file, though, because it's something built into the pre-processor.
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