Re: check file opened or not? - C / C++ / MFC Discussion Boards

Re: check file opened or not?

George_George3-Apr-08 21:18

George_George

3-Apr-08 21:18

Thanks Judy,

I think I should use ::OpenFile() with OF_SHARE_EXCLUSIVE -- the best choice. Right?

regards,
George

Re: check file opened or not?

JudyL_MD4-Apr-08 1:56

JudyL_MD

4-Apr-08 1:56

If you want to test every file under scrutiny, yes that will work. I'd try David's enum suggestion if you're looking to get a list.

Judy

Re: check file opened or not?

George_George4-Apr-08 2:19

George_George

4-Apr-08 2:19

Thanks Judy,

I only need to test for a specific file. I think OpenFile is enough, agree? Smile | :)

regards,
George

Re: check file opened or not?

JudyL_MD4-Apr-08 2:23

JudyL_MD

4-Apr-08 2:23

Yes, using OF_SHARE_EXCLUSIVE

Re: check file opened or not?

George_George4-Apr-08 2:44

George_George

4-Apr-08 2:44

Thanks JudyL_FL,

Question answered.

regards,
George

Re: check file opened or not?

led mike2-Apr-08 4:28

led mike

2-Apr-08 4:28

George_George wrote:
which API could be used to check whether a file is opened

Depends on your definition of "file is opened". An application can be displaying the contents of a file and even allowing the user to edit the contents without having an active file handle to the disk file used to persist the data. In that case there is no API that's going to tell you that, period.

led mike

Re: check file opened or not?

George_George2-Apr-08 20:37

George_George

2-Apr-08 20:37

Open I can it is used by other thread/process, they may not open the file in exclusive mode, but I need to detect whether it is used (open) or not. Any ideas?

regards,
George

Re: check file opened or not?

basementman2-Apr-08 4:55

basementman

2-Apr-08 4:55

You can try opening the file in exclusive mode.

onwards and upwards...

Re: check file opened or not?

George_George2-Apr-08 20:38

George_George

2-Apr-08 20:38

Thanks basementman!

You mean OF_SHARE_EXCLUSIVE mode of OpenFile?

regards,
George

Re: check file opened or not?

Hamid_RT7-Apr-08 4:07

Hamid_RT

7-Apr-08 4:07

I think http://www.angelfire.com/country/aldev0/cpphowto/cpp_BinaryFileIO.html[^] is helpful for you.

Re: check file opened or not?

George_George7-Apr-08 4:10

George_George

7-Apr-08 4:10

Thanks Hamid,

I looked through the link, does it relates to my original question?

regards,
George

Re: check file opened or not?

Hamid_RT7-Apr-08 4:29

Hamid_RT

7-Apr-08 4:29

I think its helpful about files,right?

Re: check file opened or not?

George_George7-Apr-08 4:38

George_George

7-Apr-08 4:38

Thanks Hamid,

It is helpful. But not direct relates to my original question. Smile | :)

regards,
George

Re: check file opened or not?

Hamid_RT7-Apr-08 5:07

Hamid_RT

7-Apr-08 5:07

Wrong DLL output

parth.p2-Apr-08 3:15

parth.p

2-Apr-08 3:15

Hi,
I have a DLL written in C and I am calling it from VB and I am using Visual Studio 6. The problem I have is that I'm trying to receive RANDOM number from C and add to my VB form. But the number received is not random or is way to big than what I pass into the parameter.

Here's the Code for .CPP

<br />
#include "stdafx.h"<br />
#include <stdlib.h><br />
#include <stdio.h><br />
#include <time.h><br />
<br />
<br />
<br />
BOOL APIENTRY DllMain( HANDLE hModule, <br />
                       DWORD  ul_reason_for_call, <br />
                       LPVOID lpReserved<br />
					 )<br />
{<br />
    return TRUE;<br />
}<br />
<br />
int _stdcall rndNum(int iMaxNum)<br />
{<br />
	int iNum;<br />
	//srand( (unsigned)iMaxNum );<br />
<br />
<br />
	srand( (unsigned)time( NULL ) );		<br />
<br />
<br />
	iNum =  rand() % iMaxNum;<br />
	<br />
	return iNum;<br />
<br />
}<br />
</time.h></stdio.h></stdlib.h>

.DEF file

<br />
LIBRARY CdllRndNum<br />
<br />
EXPORTS<br />
rndNum @1<br />

VB Code

<br />
Private Declare Function rndNum Lib "F:\Year - 2\CdllRndNum\Debug\CdllRndNum.dll" (ByRef iMaxNum As Integer) As Integer<br />
<br />
Sub AddNums()<br />
Dim i As Integer<br />
For i = 0 To 40<br />
    <br />
    List1.AddItem rndNum(100)<br />
<br />
Next i<br />
<br />
End Sub<br />

Result VB:

28156
28156
28156
28156
28156 and same and same again....

Result C:

Number is 30
Number is 43
Number is 16
Number is 24
Number is 25
Number is 63
Number is 62
Number is 84
Number is 40
Number is 64
Number is 77
Number is 79
Press any key to continue

The C code gives me perfect results in C Console app. But not in VB. Anyone any idea what is going wrong?? Confused | :confused:

- Stop thinking in terms of limitations and start thinking in terms of possibilities -

Re: Wrong DLL output

Cedric Moonen2-Apr-08 3:18

Cedric Moonen

2-Apr-08 3:18

I am far from being a VB expert, but shouldn't you pass the integer ByVal instead of ByRef ? Did you try to debug the dll to see which number you receive and what you are returning ?

Cédric Moonen
Software developer

Charting control [v1.3]

Re: Wrong DLL output

parth.p2-Apr-08 3:22

parth.p

2-Apr-08 3:22

I am not actually sure how to debug DLL :s

- Stop thinking in terms of limitations and start thinking in terms of possibilities -

Re: Wrong DLL output

C^hris L^osinger2-Apr-08 3:27

C^hris L^osinger

2-Apr-08 3:27

here's how i debug DLL + VB situations:

1. in the C++ project, "run" the DLL.
2. VS will prompt you for a debug target. tell it to run VB.exe (VB itself)
3. when VB opens, open your VB application
4. put a breakpoint on the call to your DLL
5. run your VB app

now you can step into your C++ DLL

image processing toolkits | batch image processing

Re: Wrong DLL output

Cedric Moonen2-Apr-08 3:29

Cedric Moonen

2-Apr-08 3:29

Quoted from this page[^]:
One important note is that all parameters must be passed with the ByVal keyword. This is because Visual Basic always passes parameters ByRef by default. Since C/C++ usually passes by value, this must be specified in the Visual Basic declaration. This is all that is necessary when standard C variable types (int, long, etc.) are used, however complex data types like strings and arrays require more overhead on both the client and DLL sides.

They also specify that a VB integer correspond to a short in C/C++. So, change the C function to accept a short and check if it works (and don't forget the ByVal).

Cédric Moonen
Software developer

Charting control [v1.3]

Re: Wrong DLL output

parth.p2-Apr-08 3:42

parth.p

2-Apr-08 3:42

Hi first of all thanks for quick reply. Smile | :)

Some how I realised that the speed of DLL and EXE could vary, so now I have timer which will get number every second. AND I did what you just said and now it's giving me random number between 0(1) - 100 (never seen 0 or 100) but yeh. But what happens now is that the numbers comes in ascending order.

2
12
43
56
78
90
95
1
3
5
and so on...

What surprises me most is that the same code works perfect with C but not with VB. Confused | :confused:

- Stop thinking in terms of limitations and start thinking in terms of possibilities -

Re: Wrong DLL output

David Crow2-Apr-08 3:33

David Crow

2-Apr-08 3:33

Cedric Moonen wrote:
...but shouldn't you pass the integer ByVal instead of ByRef ?

I don't see this making any difference since the ByVal/ByRef keyword only affect how the argument is sent to rndNum(), not what type of value is returned from it.

"Love people and use things, not love things and use people." - Unknown

"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne

Re: Wrong DLL output

Cedric Moonen2-Apr-08 3:37

Cedric Moonen

2-Apr-08 3:37

I don't know how it is implemented in VB, but if the ByRef is in fact passing the address of the variable, then this is the problem because that will have an impact on what the function returns (because the random number will be between 0 and that number).

Cédric Moonen
Software developer

Charting control [v1.3]

Re: Wrong DLL output

David Crow2-Apr-08 3:23

David Crow

2-Apr-08 3:23

killerp wrote:
...I'm trying to receive RANDOM number from C and add to my VB form.

Unless this is just a test to see if the two can communicate, or you are just wanting to see how a DLL works, why not just let your VB app generate its own random numbers?

killerp wrote:
But the number received is not random...

How are you verifying this?

killerp wrote:
But the number received is...way to big than what I pass into the parameter.

This statement makes little sense. The argument passed to rndNum() is simply used to seed the random number generator. It has no bearing on anything else.

"Love people and use things, not love things and use people." - Unknown

"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne

Re: Wrong DLL output

parth.p2-Apr-08 3:30

parth.p

2-Apr-08 3:30

I'm doing bit of research on random numbers from different language, and I am already using VB, C# and C So I see what you are trying to say, but I want to use this.

- Stop thinking in terms of limitations and start thinking in terms of possibilities -

Re: Wrong DLL output

parth.p2-Apr-08 4:18

parth.p

2-Apr-08 4:18

Hi,
Thanks for reply.

I haven't got any special method to verify the numbers received... It's just common sense to recognise Random numbers.

The other thing I figured out just now is that the problem lies in

srand( (unsigned)time( NULL ) );

I just removed this line and everything is working as I expected! But now i will get same numbers every time I use it. This simple dll is becoming more and more complicated...

- Stop thinking in terms of limitations and start thinking in terms of possibilities -

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