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When I create my worker thread and pass a char array, will my data be lost if in my main app I wrote over my char array with new data? Here is my thread creation code:
<br />
CWinThread* thread = AfxBeginThread(MyIOThread, this, THREAD_PRIORITY_NORMAL, 0, CREATE_SUSPENDED);<br />
thread->m_bAutoDelete = TRUE;<br />
thread->ResumeThread();<br />
<br />
Here is my worker code:
<br />
UINT CLAQTermDlg::MyIOThread(LPVOID pParam )<br />
{<br />
CLAQTermDlg * myDlg = (CLAQTermDlg *)pParam;<br />
<br />
::MessageBox(NULL, myDlg->sText, "In my Thread", MB_OK );<br />
return 0;
}<br />
Will the myDlg->sText be over written if in my main app I write over it with something else?
Thanks
Tom Wright
tawright915@yahoo.com
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Yes. Threads share the same memory space as the other threads within the program.
Worse, if you modify that same string from your main thread and worker thread at the same time, you might get some unprdictable and undesireable results.
Data access like that should be protected with a CriticalSection.
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Blake two quick questions
1. Would I put my critical section around my char array before I make my call to AfxBeginThread, or do it in my thread around the myDlg->sText char array.
2. Would it be wise to have another char array in my thread that I move this data off to and release my critical section?
Sorry I forgot a question.....If I create a char array in my thread does it have it own unique memory space each time a thread is created?
Thanks
Tom Wright
tawright915@yahoo.com
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1. You need to protect a string at the time the string is accessed.
If you really want to display the messagebox, I would make a local copy, but protect the copy process with the critical section.
UINT CLAQTermDlg::MyIOThread(LPVOID pParam )
{
CLAQTermDlg * myDlg = (CLAQTermDlg *)pParam;
CString csMessage;
EnterCriticalSection(...);
csMessage = myDlg->sText;
LeaveCriticalSection(...);
::MessageBox(NULL, csMessage, "In my Thread", MB_OK );
return 0; //Thread completed successfully
}
2. If you need the data longer, then make a variable as part of your thread class or a local variable in the thread function, and perform a protected copy, similar to above example. You also need to use same critical section in other parts of your code wherever the myDlg->sText is modified or accessed.
3. The array would be unique if it is local to the thread function or else if it is a member variable of a derived thread class, since you would be creating an instance of the thread class for each thread which is run. Just don't declare the member variable as static or it is shared among all instances of a class.
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I'm trying to write a program that is based off of data from a database program. The only problem is, I want data from the database program that is only available if I print it to the printer. However, I can choose the 'print to file' option and the information is put in a .prn file. My question, then, is does anybody know how to read from a .prn file in C++? Some characters may be readable, but others are junk.
Danny
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I did something 10 or 15 years ago, using Borland Turbo C++3, to clean up an OS-2 print file, so I could use it in DOS / Windows 3.1. The problem was that my OS-2 print-to-file contained tables, etc, which did not translate well to the Windows default character set.
As far as I remember, my approach was brute force, and it worked quite nicely! Basically, the flow was something like:
do while not EOF()<br />
read character from file as a byte value<br />
if character is a special character<br />
replace special character with standard character<br />
do something with character<br />
Some points worth noting:
1. This is a lot easier (fewer strange characters) if you choose a really simple printer - install a Generic / Text only printer in Windows.
2. I decided how to deal with special characters by doing a simple print to a printer and the same print to a file, and comparing the print file with the paper copy. This was in DOS days, so I also had to take care of converting the PC line-drawing characters to "|", "-", "+", etc.
3. According to my flow above, it may be easiest (least change to your existing program) to create a temporary "cleaned" text file from the print file, then use the cleaned file as input to your file-to-database program.
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Thanx, I'll see what I can do with this. Right now, in the file, I see a bunch of those funny boxes, but maybe my program will be able to read something from them.
Yesterday is history
Tomorrow's a mystery
Today is a gift
That's why they call it the present.
Danny
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Good luck.
As I indicated, a key part of what I did was to read the print file byte by byte as unsigned char, identify "bad" values, and replace "bad" values with "good" values using a Switch statement.
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i want during writing code on the vc6 editor to press a short cut and get a color picker panel and
choose one of those color so its hexadecemal code is written in the editor how can i do this
how do i add this capability to vc6 editor if it is not found ?
MSaty Bottom Up Gamer
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There is a common dialog class for the color picker that you're used to seeing. It's also possible to write your own, there are at least a couple that do HLS here on code project.
Christian Graus - Microsoft MVP - C++
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and how can i make this dialog class run in the editor of the visual studio 6 environment, i mean
while i am writing code to any program i want the dialog class to be a feature in the visual studio
environment, righ click and one of those pop up options is _ color picker _ i hope my question is
clear...;)
MSaty Bottom Up Gamer
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Well, then you'd have to write a visual studio add in. The question would be - why ?
Christian Graus - Microsoft MVP - C++
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Hi im trying me on Debugger
I´ve injected a dll into a Application. I can see the assambler code ( using engine to convert from binary code ) and I can list all dlls that this app uses.
My next step is to getting all thread of an application. I searched here and looked on MSDN but i cant get the information i searched.
How to get the ThreadID, ThreadEntry and Data Block of all thread in a process ?
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How about the Thread32First()/Thread32Next() pair?
"Ideas are a dime a dozen. People who put them into action are priceless." - Unknown
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What are you doing with a DLL injected into the process?
1. Why don't you use the supplied OS APIs that enable you to debug?
Debugging API[^]
These APIs enable you to write a debugger, they don't write it for you. So it's no easier using them than it is doing what you are currently doing. The only thread you would ever need to create in the process would be "debugbreakpoint" to break into the application and debug it. Sure you could manually attempt to freeze all threads and things without the debug API, however those are trivial tasks that are already implemented. Why not spend your time enabling features than implementing the most basic of functionalities.
2. You shouldn't be calling any "debugging" functions from inside the process.
Why? Because this application is being debugged. You don't know the state of the process and you are affecting it by being in the same memory space. If you freeze all the threads as well (Which is what generally occurs with debugging) you then have the problem that if one thread is say holding a heap lock in the middle of an allocation, you could deadlock your debugging thread. The debugger should be seperate from the application.
Creating a basic debugger[^]
8bc7c0ec02c0e404c0cc0680f7018827ebee
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If you already are using the debug API, then like I said everything you are doing can be accomplished from a seperate process no need for DLL Injection.
8bc7c0ec02c0e404c0cc0680f7018827ebee
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Well I never informed me about the debug api. In my oppinion it was the easiest way. With my Method theres no need to reset the debugging flag ( There are many Apps that detect if a debugger is active ). But after reading the Article you´ve post i must think about my concept. Thx for help.
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You can use the debugger to set the debug flag to 0, so you can fool those apps. What's the difference? Well, certain breaks will be skipped however any break points will be hit. But, some debug code may check the flag before doing an int 3, that's the only thing you loose (Which may have a problem when attempting to hard-break into the process, if this flag is checked.) otherwise, it doesn't really mean anything and doesn't make it so you can't debug. The debugport is an LPC that is actually on the kernel data structure, so unless they have a driver that checks the internal kernel process structure, they wouldn't know if they were being debugged after you unset the debug "boolean" in the PEB.
8bc7c0ec02c0e404c0cc0680f7018827ebee
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I have an app I'm developing that is experiencing problems when I am shutting down threads. It IS NOT MFC. I have created my threads using CreateThread().
The problem only happens in release mode. Since, my last release, I added several new threads. Here's a rough example.
Thread A creates Thread B. Thread B creates threads C, D, and E. Threads C, D, and E are timed threads. One checks disk space every 5 minutes, the other two perform a filter match check every 1/2 second and 2 seconds.
The problem is that Thread A, tells Thread B to quit. Thread B tells threads C, D, and E, to quit exactly the same as how they were created. But, my timed threads are written as:
while ( !fDone && !rtnState )
{
dwRes = ::WaitForSingleObject(ghThreadExitEvent, 300000);
switch(dwRes)
{
case WAIT_TIMEOUT :
if(gbRecording)
rtnState = CheckDiskSpace();
.
.
.
.
So, you can see that I am using WAIT_TIMEOUT and then exiting upon a ThreadExitEvent (my event). I thought that if I SetEvent() the ThreadExitEvent, that it would exit, but it's not. I also tried using a global boolean variable to flag that its time to exit to no avail.
Consequently, I started reading and I came across something that said there was a bug with WaitForSingleObject() and that WaitForMultipleObjects() was better.
So, I started looking at semaphores and mutexes. But, the example I found for semaphores was CSemaphore (MFC). Acckkk! But, I did find a sample for mutexes which sounded cool but was confused as to how I can use this object to signal that I wanted to kill an individual thread. I understand that it can start out signalled and threads can claim ownership and upon calling ReleaseMutex(), that it will transition from the non-signalled to the signalled state. Then, another thread can claim ownership, ad nauseum. But, what I want is some sort of synchronization device that will stay non-signalled until my main thread, puts it in a signalled state, and then all threads WaitingForMultipleObjects() can see it and exit the program.
Any suggestions or clarifications???
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My immediate guess is that you've made ghThreadExitEvent an auto reset event, not a manual reset event.
I know of no bug in WaitForSingleObject() and have used it quite extensively using the very technique you are using.
Anyone who thinks he has a better idea of what's good for people than people do is a swine.
- P.J. O'Rourke
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Yes, I did set it for auto reset event. Bear with me because I've never used manual reset, so, If I set it to manual, I'd have to call ResetEvent() in each thread that is getting killed, before it actually exits the thread. Does that mean I also have to call SetEvent() again from within that same exiting thread or so that the other threads see the same event?
I'm confused as to if u set an event, does one or more threads see the event or does only the first thread that handles it (gobbles it up so that) the other threads waiting for the same event don't see it.
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This is from MSDN:
When the state of a manual-reset event object is signaled, it remains signaled until it is explicitly reset to nonsignaled by the ResetEvent function. Any number of waiting threads, or threads that subsequently begin wait operations for the specified event object, can be released while the object's state is signaled.
When the state of an auto-reset event object is signaled, it remains signaled until a single waiting thread is released; the system then automatically resets the state to nonsignaled. If no threads are waiting, the event object's state remains signaled.
Seems like if you make a manual-reset event, all your threads will get the 'exit' signal.
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Thank you both, Blake and Joe. This explanation makes sense. Now, I understand why it didn't work for an auto-reset event.
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Hello all. How can I export a template class from a simple DLL? I'm using Visual C++ 7.
One day you'll find
that I have gone,
for tomorrow may rain, so
I'll follow the sun...
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A template is an abstraction and cannot be exported. You can either declare explict types of uses or write a non-template base class, export that and use the template as a wrapper. (I've used both methods.)
Anyone who thinks he has a better idea of what's good for people than people do is a swine.
- P.J. O'Rourke
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