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I need some help. Here it the whole code snippet:
#include "stdafx.h"
template<typename T>
int IndirectFunction(int * pData)
{
return 0;
}
//also tried
//int __cdecl IndirectFunction(int * pData)
//{...}
typedef int (*ONEPARAMFUNCTION)(void* param);
//also tried
//typedef int (__cdecl *ONEPARAMFUNCTION)(void* param);
int main()
{
// <<<<<<<<<
//error C2440: 'type cast' : cannot convert from 'overloaded-function' to 'ONEPARAMFUNCTION'
ONEPARAMFUNCTION t = (ONEPARAMFUNCTION) &IndirectFunction<int>;
// >>>>>>>>>
return 0;
}
How can I make it work ??
I tried googling a little - C2440 seems to be pretty "popular" but I didn't find anything that could help me.
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vccore/html/C2440.asp also didn't help 
Seems it happens becouse of the template, if I remove it compiles ok (using only - int IndirectFunction(int * pData) without the template<>).
If I replace:
int IndirectFunction(int * pData)
with
int IndirectFunction(void * pData)
it compiles ok.
If I use templates and int* as parameter I get the error. Help!
-- modified at 14:22 Friday 21st October, 2005
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try:
int (*ONEPARAMFUNCITON)(int*) = IndirectFunction<int>;
then:
int x(666);
cout << ONEPARAMFUNCITON(&x) << endl;
should work!
-- modified at 15:11 Friday 21st October, 2005
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And it works perfectly!
I would never think of this on my own - it looks wierd, but it works!!
Thank you so much!
H.
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This is normal when using templates.
The compiler only creates functions that are needed in your program.
Son you can't create a function pointer to such function until it exists.
When you first write funtion<int>(666); the compiler creates
such function. Later you can get a function pointer from it.
It seems odd but this is the way it needs to be done, with some sort of dummy call to the function
Hope this explains the wierd behaveior
codito ergo sum
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| Quote:
>When you first write funtion<int>(666); the compiler creates
such function. Later you can get a function pointer from it.</blockquote>
But that isn't what is happening (atleast I don't see it) - I first take the pointer and then call the function. And it works if I take the pointer to a function that has the exact signature, that is the int* parameter. The problems are created when I try to get a pointer to function and cast it to a function that takes a void* in the same command/line.
template<typename T>
int IndirectFunction(int * pData)
{
return 0;
}
typedef int (*ONEPARAMFUNCTION_PVOID)(void* param);
typedef int (*ONEPARAMFUNCTION_PINT)(int* param);
int main()
{
ONEPARAMFUNCTION_PINT pF0 = &IndirectFunction<int>; // ok!!
ONEPARAMFUNCTION_PINT pF = IndirectFunction<int>; // ok!!
ONEPARAMFUNCTION_PVOID pF2 = (ONEPARAMFUNCTION_PVOID)IndirectFunction<int>; // error!!
ONEPARAMFUNCTION_PVOID pF3 = (ONEPARAMFUNCTION_PVOID)pF; // ok!!
ONEPARAMFUNCTION_PVOID pF4 = (ONEPARAMFUNCTION_PVOID)(ONEPARAMFUNCTION_PINT)IndirectFunction<int>; // ok!!
int a =5;
pF(&a);
pF2(&a);
pF3(&a);
pF(&a);
return 0;
}
The wierd part is that this works:
ONEPARAMFUNCTION_PVOID pF4 = (ONEPARAMFUNCTION_PVOID)(ONEPARAMFUNCTION_PINT)IndirectFunction<int>; // ok!!
But this won't work:
ONEPARAMFUNCTION_PVOID pF2 = (ONEPARAMFUNCTION_PVOID)IndirectFunction<int>; // error!!
But isn't this practicaly the same?
IndirectFunction<int> should have the same signature as the ONEPARAMFUNCTION_PINT so the cast shouldn't be needed and the second example should be the same as the first one (I even tried forcing the same calling convention, but MSVC7 still thinks that ONEPARAMFUNCTION_PINT and IndirectFunction<int> have different signatures and requires the cast to ONEPARAMFUNCTION_PINT first) ???
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I have taken your code and everything compiles without errors.
But guess what  , I have used MSVS 2005 (MS VC8) so this is certainly a bug in the VC7 compiler.
So your code is right but your compiler (I use the same at work  ) missed the pedals, happens to the best of us
codito ergo sum
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BadKarma wrote: I have used MSVS 2005 (MS VC8) so this is certainly a bug in the VC7 compiler.
VC8 is probaby the only compiler I haven't tried
VC7.1 - same error
VC6 - more errors, oh well
GCC3.2 - same error
Thanks for your help
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In one of my classes (on programming in Scheme) my professor said that C++ is an "unsafe language". Could anyone help explain what that really means? I tried googling it, without much luck. Thanks.
-Ken Maz
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Try googling unsafe for C# and you'll se what is considered to be unsafe.
Some of the "unsafe" things are:
-variables don't have to be initialised before use
-you can cast pretty much anything to anything else
-pointers are generaly unsafe
-normal arrays are not bounds checked and can owerflow
-a milion more things...
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Thanks for the response.
-Ken Maz
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Yeah, basically, C++ allows you to do a lot of things that could potentially be dangerous, like accessing out of the bounds of an array, and leaves it up to the programmer to make sure the program is doing what he wants it to do.
Danny
The stupidity of others amazes me!
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Ken Mazaika wrote: In one of my classes (on programming in Scheme) my professor said that C++ is an "unsafe language".
Make sure you fully understand in what context he was talking. Otherwise, you could treat that as a blanket statement and come away with a completely misguided view of a very good language.
"Take only what you need and leave the land as you found it." - Native American Proverb
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Try using RegisterHotKey for receiving Win+D or a global hook.
I don't know how you could respond to that specific button, but quick launch bar is fully customisable and you could add a shorcut to an application that would show your application (or even a shorcut to the application itself).
-- modified at 13:49 Friday 21st October, 2005
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Or one other idea, don't do it. The user of windows expects that clicking the desktop icon on using WINDOWS + D keys to hide ALL windows, including your application. To play with Windows expected functionality can be kind of cheating the user.
Danny
The stupidity of others amazes me!
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bugDanny wrote: To play with Windows expected functionality can be kind of cheating the user.
I agree. Users expect their Windows applications to have a common intuitiveness. To alter that could have negative repercussions.
"Take only what you need and leave the land as you found it." - Native American Proverb
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Hi left a message about subclassing in Visual Studio 2003.
I got a few replies and some were helpful, but some wernt related to VS 2003.
Subclassing in VS6 is pretty easy because of the class wizards ability to bind the new class to the control on the dialog or window.
However in VS 2003 it doesnt have that!
Here is the url for the previous post ->
click here
Thanks Tom
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just create two empty text files, type your header code in one, and your implementation in the other. voila!
Cleek | Image Toolkits | Thumbnail maker
-- modified at 13:33 Friday 21st October, 2005
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Ignoring the IDE fluff, it works the same way - you can do it manually using ctrlWrapper.SubclassDlgItem(), or you can just add a DDX_Control() entry to your dialog class's implementation of DoDataExchange().
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Hi and thanks for the replies and for calling me a dumbass  (being sarcastic)  .
I'll give two examples of what ive being trying to achieve, for the smartasses.
Firstly, I was trying to derive a PictureBox that could be drawn in easily.
I thought i could derive a static and add OnPaint and give it a device context.
In Visual Basic 6 (my previous language) i could use a text box then use GetDC to draw in it.
Secondly, I was trying to create a NumberBox from a EditBox and catch the WM_CHAR message and only allow Digits. The NumberBox class was derived from the EditBox Class.
Thanks again
Tom
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Tom Moore wrote: I thought i could derive a static and add OnPaint and give it a device context.
That'll work. Instantiating CPaintDC in an OnPaint handler will give you a DC you can draw onto. You probably also want to implement OnEraseBknd, if only to ensure that nothing extra gets drawn there.
Tom Moore wrote: Secondly, I was trying to create a NumberBox from a EditBox and catch the WM_CHAR message and only allow Digits.
There are a few classes like that already written - do a search on CP. Note that if you only need integers, you can use the ES_NUMBER style and the standard control will take care of it for you.
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cool! If i derive my new class from the parent class!
Eg. class CDrawBox : public CStatic or CNumberBox : public CEdit
Do i subclass the Static Picture box on the form using SubClassDlgItem, same goes for the Numberbox. Thanks again
Tom
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Tom Moore wrote: Do i subclass the Static Picture box on the form using SubClassDlgItem
You can, or you can just use MFC's built-in subclassing, which uses DoDataExchange() and DDX_Control to do the same thing. Take a bit of time and look through the demo code for this article:
http://web4.codeproject.com/staticctrl/digidisplay.asp[^]
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