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See if either of these two articles help:
http://flounder.com/screencapture.htm
http://flounder.com/printbitmap.htm
"The pointy end goes in the other man." - Antonio Banderas (Zorro, 1998)
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Thanks a lot, u read me well, I will check it an let u know
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Hi,
I am struggling to convert some functions from a C++ DLL to some function references in VB.net
I dont program in C++, so I am hoping someone can help me with converting a couple of function prototypes:
This are the C++ prototypes:
CP2101_Open(DWORD dwDevice, HANDLE* cyHandle);
CP2101_GetProductString(DWORD dwDeviceNum, LPVOID lpvDeviceString, DWORD dwFlags);
CP2101_Close(HANDLE cyHandle );
This is what i have in vb.net:
Public Declare Function CP2101_Open Lib "CP2101.dll" (ByVal DeviceNum As Long, ByRef Handle As Long) As Integer
Public Declare Function CP2101_GetProductString Lib "CP2101.dll" (ByVal DeviceNum As Long, ByRef DeviceString As String, ByVal Options As Long) As Integer
Public Declare Function CP2101_Close Lib "CP2101.dll" (ByVal DeviceNum As Long) As Integer
I am not sure that I am converting the pointer data types correctly etc from C++ to Vb.net. If some could check my work.
Thanks
Barry
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What problems are you experiencing here?
The VB declarations look OK to me. 
Ant.
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These
nelsonbd wrote:
This are the C++ prototypes:
not true!
These are C prototypes, else they would have very crazy export names in C++ name convention!
Don't try it, just do it! 
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The potential problem I see is in interpreting the LPVOID DeviceString as a ByRef String. If I remember my VB right, a ByRef String is passed to a C function as a pointer to BSTR. That may not be (probably is not) what the C function is expecting.
An LPVOID doesn't give very much information about what it is expecting: it could be a null-terminated string, a null-terminated wide-string, a BSTR or perhaps a pointer to BSTR. Do you have source for that C function, or a C example of its use?
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Firstly, you should normally use System.IntPtr for opaque pointer types when using VB.NET. This will help you if you ever port to 64-bit (the IntPtr type is 32 bit in a 32-bit process but 64 bits in a 64-bit process).
As for CP2101_GetProductString, if the C/C++ code is interpreting the lpvDeviceString parameter as a string, you should use
Public Declare Function CP2101_GetProductString Lib "CP2101.dll" ( _
ByVal DeviceNum As Long, _
ByVal DeviceString As String, _
ByVal Options As Long) As Integer ByRef indicates an in/out parameter. If the function alters this data, you should use a StringBuilder object instead (still passed ByVal), and set its Capacity to the maximum size you expect the function to write.
If you're getting MissingMethodExceptions, your DLL's exports may be mangled. To verify this, use dumpbin /exports. If the output contains ? characters and no recognisable function names, the names are mangled. You have two choices. Either you can rewrite your declarations to use the DllImportAttribute rather than Declare, and use the EntryPointName property to indicate the mangled name, or you can specify extern "C" in front of the exported function declarations to tell the compiler not to mangle the names. Remember that the latter will break binary compatibility with any existing clients.
Stability. What an interesting concept. -- Chris Maunder
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Hi guys,
A question:
I got a class A that has a overridden copy constructor and assignment operator.
I derive class B from A.
*If B does not have an overridden copy constructor or assignment operator will the assignments of objects of class B invoke the copy constr. or assign operator of class A for the A part of class B(if you know what I mean)?
eg:
class A
{
class A();
class A( const A& a);
A& operator=(const A& a);
...
};
class B: public A
{
...
};
int main()
{
B obj1, obj2;
...
obj2 = obj1; //is operator= of class A called?
B obj3 = obj2; // is copy construct of class A called?
}
Greetings,
Davy
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no, you ll have to modify like this
B obj1;
A obj2;
obj2 = obj1; //operator= of class A is called
A obj3 = obj2; //copy construct of class A is called
but remember ur objects will have to be sliced..
greatest thing is to do wot others think you cant
suhredayan@omniquad.com>
messenger :suhredayan@hotmail.com
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Suhredayan P wrote:
ur objects will have to be sliced..
woah whats that ? 
MSN Messenger.
prakashnadar@msn.com
Tip of the day of visual C++ IDE.
"We use it before you do! Visual C++ was developed using Visual C++"
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Can you set a breakpoint on the line(s) in question to see what happens?
"The pointy end goes in the other man." - Antonio Banderas (Zorro, 1998)
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Can someone pls provide me with an algorithim that generates an random number ( 0 to 1000)and it cannot generate the same random number more than once.
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The output wouldn't be a random number as you are affecting the outcome, however to generate random numbers:
// seed the random number generator using the current time
srand((unsigned)time(NULL));
// gets a random number between 0 and 0x7fff
int iRandom = rand();
// scale this number down to a value between 0 and 1000.
iRandom /= (RAND_MAX / 1000);
Regards,
Simon
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thanks for your replay Mr.simon
but with // seed the random number generator using the current time
srand((unsigned)time(NULL));
the number will be repeated, but for me numbers shouldn't repeated in same sequence .
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You could hold all generated random numbers in a vector and check that the next number has not been used previously. If it has call the random again.
As long as you only want a few, i.e small percentage of the possible 1000 pseudo random numbers in your sequence, this will suffice.
Ant.
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The numbers will be repeated in the same sequence only if you start two copies of the application at the same time - the numbers are psuedorandom.
If that isn't good enough then you could seed the timer again each time you get a new random number - then differences such as the processor speed / load etc will mean that the sequence will definitely not be repeated.
Regards,
Simon
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Seeding the random number generator each time is a VERY BAD IDEA. For example, if you can generate 10,000 random numbers in a second, you will get the same random number each time since time only has a resolution of a second.
Also, many random number generators should be initialized with a large prime number. By not doing that, it can take a few interation before the random numbers start getting "good". Reseeding the random number generator constantly places it back in the initial condition of generating a small series of bad values.
Tim Smith
I'm going to patent thought. I have yet to see any prior art.
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Yes, my bad - I forgot that the time bit was in seconds.
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The return value of time() is the number of seconds since January 1, 1970 00:00 (or December 31, 1969 19:00). In any case, as long as its not called two successive times in less than one second, the return value will always be different so srand() will always be seeded uniquely.
"The pointy end goes in the other man." - Antonio Banderas (Zorro, 1998)
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class IncInt<br />
{<br />
private :<br />
int i_ ;<br />
public :<br />
IncInt ( int i ) : i_ ( i ) {}<br />
<br />
int operator () ()<br />
{<br />
return i_++ ;<br />
}<br />
} ;<br />
<br />
void Random1000 ()<br />
{<br />
std::vector<int> vi ;<br />
vi.resize ( 1000 ) ;<br />
std::generate ( vi.begin (), vi.end (), IncInt ( 0 )) ;<br />
std::random_shuffle ( vi.begin (), vi.end ()) ;<br />
}
Gives you vector containing 0-999 in random order. You can use a custom 'random' function as an extra argument to 'random_shuffle' if you wish. I'll leave it up to you to decide how to wrap this up, should it suit your purpose.
Paul
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or
void Random1000 ()
{
std::vector vi ;
for (int i = 0; i < 1000; i++)
vi .push_back (i);
std::random_shuffle ( vi.begin (), vi.end ()) ;
}
If you don't want all that STL obfuscation in there. Why write 15 lines of code when 2 works just fine.
Tim Smith
I'm going to patent thought. I have yet to see any prior art.
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I only had to write one line.... But it was necessary to cut and paste a bit to make it make sense here.
Anyway it's the ease of using the random_shuffle that's important. The OP didn't want a sequence of random numbers, AFAICT.
It could of course be written,
<br />
void Random1000()<br />
{<br />
int vi [ 1000 ] ;<br />
for ( int i = 0; i < 1000; ++i )<br />
vi [ i ] = i ;<br />
std::random_shuffle ( vi, vi + 1000 ) ;<br />
...<br />
}<br />
Paul
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Hi,
I want to build a module in my app that will alow me to stream the video from my webcam. Anybody knows any open source app or any article on this matter? I don't know how to start.
Thanks
-----
We are what we repeatedly do. Excellence, then, is not an act, but a habit.
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hi,
the DIJOYSTATE2 struct is used to retreive the current state of a gamepad.
two members are standardized (lX, lY). when i say standardized i mean that you can localize a human readable equivalent ("left", "right", "up", "down" in english ; "gauche", "droite", "haut", "bas" in french ; etc).
for other members i didn't find a way to localize them since from a gamepad to another the same member can map a different axe....
is there a function in DirectInput that could help me on this case ??
any hint/suggestion is welcome.
thanks.
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