global buffer or passing by reference?

[billiam904]

First, I am new to C++. I have some C background with DOS and Unix but that was 15 years ago. My most recent work was vb.net. I am now doing some audio based coding in VC++ and I am having some problems, probably from my lack of knowledge. Unfortunately, I have until Monday to get this code working... I have three classes and three separate files. The developer that started this is simply calling the classes without reinstantiating them. I am reading a wave file in and that works fine. But, I need to create a global buffer for the wave data so that the other two classes can access it or find someway to pass the buffer by references to the other classes' functions. Can anyone give me some same code on doing this? Thank you. Bill Dennis Orlando, FL

[khan]

Create a class for the global data buffer. Put it in a separate header file. class CGlobalData { static [DATA_TYPE_HERE] m_Data; }; Then use it as: CGlobalData::m_Data; this is this.

[billiam904]

I did as you suggested and am etting the following error: c:\development\c-tools\Classes\WavWrite.cpp(79): error C2248: 'CReadDemoWave::testinteger' : cannot access private member declared in class 'CReadDemoWave' I need to be able to access this data from three separate .cpp files. Here's my 'h: \ class CReadDemoWave { static int testinteger; public: void ReadDemoWave(); void ReadDemoIntoBuffer(); void PlayWav(); long QueueWaveData(HWAVEOUT HWaveOut, WAVEHDR * waveHeader, DWORD WaveDataPlayed, DWORD WaveBufSize, HMMIO HMmio); LPSTR *GetDemoBuffer(void); void WriteDemo(HMMIO recordHandle); WAVEHDR lpDemoData; DWORD dwDemoDataSize; int m_nDemoBufferSize; BYTE* m_pbyDemoBuffer; HMMIO m_hmmio; }; I am including the .h in all three .cpp files. Am I doing something wrong? Bill Dennis Orlando, FL

[khan]

Sorry about that. You need to make the variable public. By default it is private. Just write public: before the variable declaration in the class. Like: class CSomething { public: //this needs to be inserted. static DATA_TYPE m_Data; }; this is this.

[Achim Klein]

Hi, in my opinion it is always worth an attempt to get around global data. Maybe this design pattern (Visitor) can help you. The class that can read wave files:

class IveGotTheData
{
public:

// add some 'Getter' methods here

bool ReadWaveFile(const char* Path);

void UseMyData(IknowTheAlgorithm& Operator)
{
Operator.Operate(this);
}
};

The base class for all algorithms that modify your wave data (the Visitor):

class IknowTheAlgorithm
{
public:

virtual void Operate(IveGotTheData* Data) = 0;
};

Your first algorithm is encapsulated in this class:

class Algorithm1 : public IknowTheAlgorithm
{
public:

virtual void Operate(IveGotTheData* Data)
{
// your first algorithm goes here
}
};

Your second algorithm is encapsulated in this class:

class Algorithm2 : public IknowTheAlgorithm
{
public:

virtual void Operate(IveGotTheData* Data)
{
// your second algorithm goes here
}
};

Using your algorithms looks like this:

void main()
{
IveGotTheData wav;

if (wav.ReadWaveFile("Test.wav"))
{
Algorithm1 alg1;
Algorithm2 alg2;

  wav.UseMyData(alg1);
  wav.UseMyData(alg2);

}
}

Regards Achim Klein

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We can do no great things, only small things with great love. - Mother Theresa

[billiam904]

This would be good if it were a new system or code already written in this fashion but I am modifying someone else's code, so I can';t totally rewrite the program. But, thanks. Bill Dennis Orlando, FL

[billiam904]

I'm sorry but now I get the following message: Single error LNK2001: unresolved external symbol "public: static int CReadDemoWave::testinteger" (?testinteger@CReadDemoWave@@2HA) Here is my .h: #include #include #include #define ERROR_LENGTH 1024 class CReadDemoWave { public: static int testinteger; void ReadDemoWave(); void ReadDemoIntoBuffer(); void PlayWav(); long QueueWaveData(HWAVEOUT HWaveOut, WAVEHDR * waveHeader, DWORD WaveDataPlayed, DWORD WaveBufSize, HMMIO HMmio); LPSTR *GetDemoBuffer(void); void WriteDemo(HMMIO recordHandle); // =========== D == E == M == O ======================= // BD create demo buffer. WAVEHDR lpDemoData; DWORD dwDemoDataSize; int m_nDemoBufferSize; BYTE* m_pbyDemoBuffer; HMMIO m_hmmio; //HMMIO hmmio; char m_szError[ERROR_LENGTH]; int m_nError; MMIOINFO m_mmioInfo; DWORD dwDataSize; DWORD dwCount; HPSTR m_hptr; int m_nBufferSize; }; Bill Dennis Orlando, FL

[Achim Klein]

Hi, the problem here is that the definition is missing. Guess your header file (ReadDemoWave.h) looks like this:

class CReadDemoWave
{
public:

// Construction

// Getter methods

// Setter methods

private:

// Attributes

static int m_anyInt; // this is just a declaration
};

Then you have to add the definition of m_anyInt to your cpp file:

#include "ReadDemoWave.h"

// define your static attributes
int CReadDemoWave::m_anyInt;

CReadDemoWave::CReadDemoWave()
{
// your constructor code
}

// Getter methods

// Setter methods

Regards Achim Klein

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We can do no great things, only small things with great love. - Mother Theresa

[Achim Klein]

Hi, could you post the three header files, please ? Maybe <pre> code </pre> is useful.

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We can do no great things, only small things with great love. - Mother Theresa

[billiam904]

////////////////////////////////////////////////////////////////////// // WavWrite.h: interface for the CWavWrite class. #if !defined(AFX_WAVWRITE_H__2C400A28_DDC3_11D0_9FD3_444553540001__INCLUDED_) #define AFX_WAVWRITE_H__2C400A28_DDC3_11D0_9FD3_444553540001__INCLUDED_ #if _MSC_VER >= 1000 #pragma once #endif // _MSC_VER >= 1000 #include #include #include //#include "readdemowave.h" #define ERROR_LENGTH 1024 //CReadDemoWave cReadDemo; //static DWORD dwDemoDataSize; //WAVEHDR lpDemoData; //static WAVEHDR lpDemoData; /* Definition from MS typedef struct { WORD wFormatTag; WORD nChannels; DWORD nSamplesPerSec; DWORD nAvgBytesPerSec; WORD nBlockAlign; WORD wBitsPerSample; WORD cbSize; } WAVEFORMATEX; typedef struct { FOURCC ckid; DWORD cksize; FOURCC fccType; DWORD dwDataOffset; DWORD dwFlags; } MMCKINFO; */ class CWavWrite { private: char m_szName[FILENAME_MAX]; HMMIO m_hmmioFile; HMMIO m_hmmioDemoFile; MMCKINFO m_ckRIFF, m_ckfmt, m_ckdata; int m_nDataLeft; WAVEFORMATEX *m_pwfx; PCMWAVEFORMAT m_pcmWaveFormat; int m_cbExtraAlloc; MMIOINFO m_mmioInfo; // BD 9/13/05 /*int DEMO; int rndcnt; int bufcnt;*/ // Created here so not created each time Read or Write Data is called // Otherwise these could be local variables - trade speed for size int m_nCopyLength, m_nActualWrite; int m_i; // Error variables int m_nError; char m_szError[ERROR_LENGTH]; public: //WAVEHDR lpDemoData; //DWORD dwDemoDataSize; // Constructor (empty) / Destructor CWavWrite(); virtual ~CWavWrite(); // Data processing - too large to be effective as an inline functions // BD added lat param for demo buffer //int Write(BYTE *pBuffer, int nDataSize, WAVEHDR *pDemoBuffer); int Write(BYTE *pBuffer, int nDataSize); void WriteDemo(BYTE *pBuffer, int nDataSize); // File Manipulation void Open(void); void Init(MMCKINFO *pckRIFF, MMCKINFO *pckfmt, MMCKINFO *pckdata, WAVEFORMATEX *pwfx, int nBufferSize); void Init(short wBitsPerSample, int nSampleFrequency, short wChannels, int nBufferSize); void Close(void); // Parameter Manipulation void SetName(char *); char *GetName(void); // Parameters below may be different than input file, CWavRead. long GetNumberOfSamples(void); long GetSampleFrequency(void); short GetBitsPerSample(void); short GetNumberOfCha

[Achim Klein]

Many lines. I need a moment...

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We can do no great things, only small things with great love. - Mother Theresa

[Achim Klein]

I guess you have a class named CWavRead. I guess you want to pass the buffer that this class fills to other functions. I guess all of this takes place somewhere inside your CSingleDlg class. Please correct me, if I'm wrong. In this case my header file would approximately look like this:

// forward declaration
class CWavRead;

// class definition
class CSingleDlg
{
public:

...

private:

// my dialog 'knows' an object of the CWavRead class
CWavRead* m_wavReader;
};

And my implementation file would approximately look like this:

#include "SingleDlg.h"
#include "WavRead.h"

// constructor
CSingleDlg::CSingleDlg()
{
m_wavReader = new CWavRead;
}

// destructor
CSingleDlg::~CSingleDlg()
{
delete m_wavReader;
}

// read wav file
CSingleDlg::OnFileOpen()
{
m_wavReader->read(path);
}

// modify wav data
CSingleDlg::OnEditModify()
{
// get data
long size = m_wavReader->getBufferSize();
BYTE* buffer = m_wavReader->getBuffer();

// create local (temporary) object
CWavOperator operator;

// pass the read data
operator.DoSomething(buffer, size);
}

Is it useful ?

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We can do no great things, only small things with great love. - Mother Theresa

[Achim Klein]

Unfortunately I don't know the interface of your CWavRead class...

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We can do no great things, only small things with great love. - Mother Theresa

[billiam904]

Thanks. Can you give me an idea of the implementation code for the getBuffer function to make sure I'm doing it right. I wrote one but it kepts resetting. Here's my read .h #include #include #include #define ERROR_LENGTH 1024 class CReadDemoWave { public: BYTE m_pbyDemoBuffer; static int testinteger; void ReadDemoWave(); BYTE *ReadDemoIntoBuffer(); void PlayWav(); long QueueWaveData(HWAVEOUT HWaveOut, WAVEHDR * waveHeader, DWORD WaveDataPlayed, DWORD WaveBufSize, HMMIO HMmio); BYTE *GetDemoBuffer(void); //void WriteDemo(HMMIO recordHandle); //public: // =========== D == E == M == O ======================= // BD create demo buffer. WAVEHDR lpDemoData; DWORD dwDemoDataSize; int m_nDemoBufferSize; //BYTE* m_pbyDemoBuffer; HMMIO m_hmmio; //HMMIO hmmio; char m_szError[ERROR_LENGTH]; int m_nError; MMIOINFO m_mmioInfo; DWORD dwDataSize; DWORD dwCount; HPSTR m_hptr; int m_nBufferSize; //WAVEFORMATEX waveFormat; }; Bill Dennis Orlando, FL

[Achim Klein]

If your read function fills m_pbyDemoBuffer, just write

BYTE* CReadDemoWave::getBuffer() const
{
return m_pbyDemoBuffer;
}

Returning a reference (pointer) breaks the privacy concept of your class, but it's handy.

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We can do no great things, only small things with great love. - Mother Theresa

[billiam904]

I have it like this: BYTE *CReadDemoWave::GetDemoBuffer(void) { return &m_pbyDemoBuffer; } When I take out the refrence (&), I get a compiler error saying it can't convert from BYTE to BYTE*. It's been 15 years since I've worked with pointers so not sure I am doing this correctly. My pointer seems to be resetting itself from the time the buffer is created and the time I call GetDemoBuffer(). Bill Dennis Orlando, FL

[Achim Klein]

BYTE m_pbyDemoBuffer is no array. It's just one number. If you want to create an array, please use new and delete:

int size = 1000;

// allocate memory
BYTE* array = new BYTE[size];

// free memory
delete[] array;

It's like malloc and free.

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We can do no great things, only small things with great love. - Mother Theresa

[billiam904]

In another post, I asked someone to show me how to allocate member for m_pbyDemoBuffer. I am rewading the wave data into a LPSTR variable, then creating and allocating memory for m_pbyDemoBuffer using GlobalAlloc and doing memcpy from lpDemoData.lpData to m_pbyDemoBuffer. I am then returning *m_pbyDemoBuffer in GetDemoBuffer(). So, not using arrays here. Bill Dennis Orlando, FL

[Achim Klein]

I am reading the wave data into a LPSTR variable, [...] How do you allocate the memory at the position your LPSTR variable points to ?

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We can do no great things, only small things with great love. - Mother Theresa

[billiam904]

I've pasted part of the code below. I have a lot of junk commented out in the actual .cpp file but if you want that, I can send it without violating my contract. Thanks. ''Allocate space for data in lpDemoData structure. // lpData is LPSTR. if (!( lpDemoData.lpData = (char *)VirtualAlloc(0, dwDemoDataSize<<1, MEM_COMMIT, PAGE_READWRITE))) { printf("ERROR: Can't allocate memory for WAVE buffer!\n"); } // Read Data Chunk into lpData if (readres = mmioRead(hmmio, (HPSTR )lpDemoData.lpData, dwDemoDataSize) != dwDemoDataSize) { AfxMessageBox("Error: Failed to read data chunk."); mmioClose(hmmio,0); return; } //Create byte-based buffer, allocate memory and copy // lpData to it. int lenlpData=strlen(lpDemoData.lpData); m_pbyDemoBuffer=(BYTE)GlobalAlloc(GMEM_MOVEABLE | GMEM_SHARE, lenlpData ); memcpy((BYTE*)m_pbyDemoBuffer, lpDemoData.lpData, lenlpData); Bill Dennis Orlando, FL