C / C++ / MFC

23-Sep-04 15:15

Windows calls WinMain() when your program is run, so it will set up the parameters itself.

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Help writing a function

NietzscheDisciple23-Sep-04 12:11

NietzscheDisciple

23-Sep-04 12:11

Hello All,

I am new to C++ and am trying to do some DSP programming. I would like to write the following function

y(n) = (1-a)*x(n-1) + a*y(n-1)

The arguments to this function are all floats - "x", "y" and "a".

Could somebody help me with this?

Ravi Bhavnani23-Sep-04 12:35

Ravi Bhavnani

23-Sep-04 12:35

I could help you if you can answer these 2 questions:

(1) is x a function (if so, what is it)?
(2) what's the definition of y(0)?

/ravi

My new year's resolution: 2048 x 1536
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NietzscheDisciple23-Sep-04 12:44

NietzscheDisciple

23-Sep-04 12:44

Thanks, Ravi.

To answer your questions, this function which I'll call SmoothingFunction, is called by another function by name, SmoothCoeffs().

I have two arrays, Coeff[] and Smooth[], each with 5 elements. Values in the array Coeff[] are "smoothed" and then stored in Smooth[].

Here is the SmoothCoeffs() function:
NUM_ITER is 5.

<br />
inline void cDSP::SmoothCoeffs()<br />
{<br />
   float *nStart = &gnCoeff[mnCoeffIndex];<br />
   float *nFin = &gnSmooth[mnCoeffIndex];<br />
<br />
   for (int i = 0; i < NUM_ITER; i++)<br />
   {<br />
	// CALL SMOOTHING ROUTINE<br />
	SmoothingFunction(nStart, nFin, mnSmoothCoeff);<br />
    }<br />
<br />
    mnCoeffIndex += NUM_ITER;				   // increment coeff index<br />
	<br />
   if (mnCoeffIndex >= NUM_COEFF)<br />
	mnCoeffIndex = 0;				   // reset coeff index if finished with buffer<br />
}<br />

"x" represents an element of Coeff() and "y" represents an element of Smooth().

Hope that helps!

Ravi Bhavnani23-Sep-04 13:31

Ravi Bhavnani

23-Sep-04 13:31

OK, so that implies x and y are simply floating point values and not functions. But then I'm confused by your original definition, viz:

y(n) = (1-a)*x(n-1) + a*y(n-1)

To me, that says y is a function of n, whose definition includes the value y(n-1). This is pretty easy to code recursively, but then I need to know the exit condition (eg: y(0) is arbitrarily defined as some value). Assuming y(0) is zero, I think the function you want is:

#define EPSILON   0.0000001
double y
  (float n,
   float a,
   float x)
{
  if (fabs (n) < EPSILON)
     return (0.0); // exit condition
  return ((1.0 - a)*x*(n - 1.0) + (a*y(n-1)));
}

/ravi

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NietzscheDisciple23-Sep-04 13:45

NietzscheDisciple

23-Sep-04 13:45

Hi Ravi,

I should've probably defined it as follows:

y[n] = (1-a)*x[n-1] + a*y[n-1]

y[n] and x[n] are the elements of two arrays, Smooth[] and Coeff[] respectively.

Recursive File Enumeration

Ravi Bhavnani23-Sep-04 18:07

Ravi Bhavnani

23-Sep-04 18:07

OK, it looks like you've answered your own question, then? Smile | :)

/ravi

My new year's resolution: 2048 x 1536
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wayvirgo23-Sep-04 11:50

wayvirgo

23-Sep-04 11:50

Hello, Could somebody please post a very simple function which takes a file path as a function, and recursively lists all files and folders found under that path?

I've found a few other examples on the 'net, but they seem to be focused at older C compilers, and just won't compile under Visual Studio.

If somebody could please help out with this, I'd greatly appreciate it!!!

Thanks in advance,

--Jon

Re: Recursive File Enumeration

David Salter23-Sep-04 11:56

David Salter

23-Sep-04 11:56

I think this does what you want.

http://www.codeproject.com/file/sadirread.asp

store your internet favourites online - www.my-faves.co.uk

Re: Recursive File Enumeration

wayvirgo23-Sep-04 12:08

wayvirgo

23-Sep-04 12:08

Well, sort of... I've seen that before, but I'm a newbie to C++, though very familiar with c-styled Perl, and could not boil down a simple recursive function from that to be used in a console app... Still so many things in that demo app that are so foreign to me, that I have a really hard time making heads and tales of it.

Re: Recursive File Enumeration

BlackDice24-Sep-04 3:20

BlackDice

24-Sep-04 3:20

here's an example using the CFileFind class.

 void MyClass::GetFiles(CString strPath,BOOL bRecurse)
{

	CFileFind finder;
	CString strFile;
	BOOL bWorking = finder.FindFile(strPath + _T("\\*.*"));

	while(bWorking)
	{
		bWorking = finder.FindNextFile();
		if(finder.IsDirectory() && !finder.IsDots() && bRecurse)
		{
			strFile = finder.GetFilePath();
			
			GetFiles(strFile,bRecurse);
		}
		if(!finder.IsDirectory && !finder.IsDots())
		{
			strFile = finder.GetFilePath();
			//this is a file, do something with the string
		}
	}
}

you should be able to use the function like this:
GetFiles("C:\\MyProjects",TRUE);

this should get all the files in that directory and all subdirectories.

to only get the files with one folder, just call with a second parameter of false

[insert witty comment here]

bdiamond Sleepy | :zzz:

How about this?

Tom Wright23-Sep-04 11:34

23-Sep-04 11:34

I have a BYTE array of 4 and I want to convert it to a decimal..how is this done.
Example:

<br />
BYTE SomeHex[4];<br />
<br />
SomeHex[0] = 0x00;<br />
SomeHex[1] = 0x00;<br />
SomeHex[2] = 0x27;<br />
SomeHex[3] = 0x30;<br />
//According to the windows calc hex x2730 = 10032<br />

So how do I convert this array to a decimal of 10032?
Thanks

Tom Wright
tawright915@yahoo.com

Michael Dunn23-Sep-04 11:42

23-Sep-04 11:42

Just FYI, if you're on an x86 machine, then the bytes are backwards.

You don't convert from hex to decimal, you just put the number in an int variable and use it. How you output the value (hex, octal, binary, etc.) isn't related to how the value is stored.

--Mike--
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Tom Wright23-Sep-04 11:50

23-Sep-04 11:50

So...and correct me if i'm wrong.....if I move Somehex to an int...like:

int intVal = SomeHex;

then the value in intVal will be 10032? I've tried this but I get a compiler error saying "cannot convert from BYTE[4] to int". And if I type cast it as an int then I get 0x0012f408 as a value, which is not right.

So can you explain more please?

Tom Wright
tawright915@yahoo.com

BlackDice23-Sep-04 11:59

BlackDice

23-Sep-04 11:59

How about

int i1 = (int)SomeHex[0];<br />
int i2 = (int)SomeHex[1];<br />
int i3 = (int)SomeHex[2];<br />
int i4 = (int)SomeHex[3];

or maybe try this:

int* intVal = (int*)SomeHex;<br />
int intVal2 = *intVal;

Haven't tested either one, so BEWARE. But hopefully one of these will work or get you on the right path.

[insert witty comment here]

bdiamond Sleepy | :zzz:

Tom Wright23-Sep-04 12:04

23-Sep-04 12:04

Nope.....just returning a hex value of 0x30270000, which is not right.
Thanks

Tom Wright
tawright915@yahoo.com

Michael Dunn23-Sep-04 12:03

23-Sep-04 12:03

To store the bytes into an int, I would do:

BYTE by[4] = { 0x30, 0x27, 0, 0 };
int n;
 
  n = *(int*) &by[0];

Keep in mind that the order of the bytes is CPU-specific. On x86 it's low->high as I showed above.

Tom Wright wrote:
And if I type cast it as an int then I get 0x0012f408 as a value, which is not right.

That's because a cast isn't a magical command that makes the compiler read your mind. Wink | ;)

You need to understand exactly what a cast does, and avoid just "throwing in casts" hoping to make it work. (This isn't a flame, it's a difficult subject, I know.)
Casting by to int returns the value of &by[0], which in your case was 0x0012f408

--Mike--
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Tom Wright23-Sep-04 12:24

23-Sep-04 12:24

Michael Dunn wrote:
Keep in mind that the order of the bytes is CPU-specific. On x86 it's low->high as I showed above.

I see what you are saying. Here is the value that I see when I view it thru quick watch: 0x30270000 Which is reversed from what is in the array.

Okay so if I reverse this then I'll get the right Hex value in my int.

Questions:
1. The value I see in quick watch...is this the hex value or the int value?
2. If it's the hex value then I still need to convert this to a usable int. What I mean is that this BYTE array is part of a data stream from a socket.

<br />
	struct ParseData{<br />
		BYTE STAP[4]; <br />
		BYTE BlockLen[4];<br />
		BYTE HDRLen[2];<br />
		BYTE FunctionCode[2];<br />
		BYTE ValField[4];<br />
		BYTE DataLen[4];<br />
		BYTE MsgStatus[2];<br />
		BYTE Dest[2];<br />
	};<br />
	ParseData myStuff;<br />
	memcpy(&myStuff, dataBuffer, sizeof(myStuff));<br />
	char* DataPacket = new char[myStuff.DataLen];<br />

It tells me the length of another array in the stream which is a datapacket. So this BYTE array is the packet lenght. I've set up the data packet as a char* Datapacket; Can I initialize it like this:

char* DataPacket = new char[n]; ??? Confused | :confused:

and will this be the size of 10032 or 2730?

Really I'm trying to understand this and I really appreciate your help

Thanks

Tom Wright
tawright915@yahoo.com

Tom Wright23-Sep-04 12:32

23-Sep-04 12:32

I got it..here is my code:

<br />
	BYTE NewDataLen[4];<br />
	NewDataLen[0] = myStuff.DataLen[3];<br />
	NewDataLen[1] = myStuff.DataLen[2];<br />
	NewDataLen[2] = myStuff.DataLen[1];<br />
	NewDataLen[3] = myStuff.DataLen[0];<br />
	<br />
	int nDataLength;<br />
	nDataLength = *(int*) &NewDataLen[0];<br />
	CString someString;<br />
	someString.Format("Here is the value: %d", nDataLength);<br />
	AfxMessageBox(someString);<br />

I'm sure there is an easier way to do the reverse but my model is "simplicity is best"...ah I'll tweak this as I go.

Now that I have my DataLen I can size my char array and put in my data..... Smile | :)

Thanks for the help again.

Tom Wright
tawright915@yahoo.com

Michael Dunn23-Sep-04 15:13

23-Sep-04 15:13

Glad you got it working. Smile | :)

--Mike--
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Pinky, are you pondering what I'm pondering?
I think so Brain, but how will we fit the hamster inside the accordion?