Thread: help making a reference to a pointer

Hi all,

I'm trying to keep use a reference to a pointer within a nested structure, but it isn't working. I looked in a couple books, didn't see anything that helped, so I am posting here. Hopefully someone can spot what I am doing wrong quite easily.

I have two structures:

Code:

typedef struct _smsBuffer
{
        SMSHeader *pSmsHeader;
        SMS_DATA *pSmsRecord;
} t_smsBuffer;

typedef struct _smsanal
{
        t_object x_obj; 
        t_canvas *canvas;
        t_symbol *s_filename;
        t_int i_frame, i_frameSource, synthBufPos;
        t_int nframes;
        t_float *synthBuf;
        t_float f;
	FILE *pSmsFile; 
        SYNTH_PARAMS synthParams;
        t_smsBuffer smsBuf;
} t_smsanal;

In smsBuf, pSmsRecord will be an array of frames of data records, while the header gives overall info about the frames. Now, in my function for opening a file, I get a pointer to the t_smsanal structure as x:

Code:

static void smsanal_open(t_smsanal *x, t_symbol *filename)
{
        SMSHeader *pHeader = (SMSHeader *)x->smsBuf.pSmsHeader;
        // this workes:
        //GetSmsHeader (filename->s_name, &x->smsBuf.pSmsHeader, &x->pSmsFile)
        // but this doesn't (crashes):
        GetSmsHeader (fullname->s_name, &pHeader, &x->pSmsFile)
}

I'd really like to use the simple pointer to the header, since I will constantly need to be getting data out of it in later code. But nothing I seem to try works.

Thanks if you can help,
Rich

As for the (SMSHeader *) cast, it is only there because I was trying to see if it would help, but didn't. I guess it isn't doing anything.

Here is GetSmsHeader:

Code:

int GetSmsHeader (char *pChFileName, SMSHeader **ppSmsHeader,
                  FILE **ppSmsFile)
{
	int iHeadBSize, iRecordBSize, nRecords;
	int iMagicNumber;
    
	/* open file for reading */
	if ((*ppSmsFile = fopen (pChFileName, "r")) == NULL)
		return (SMS_NOPEN);
            
	/* read magic number */
	if (fread ((void *) &iMagicNumber, (size_t) sizeof(int), (size_t)1, 
	           *ppSmsFile) < (size_t)1)
		return (SMS_RDERR);
	
	if (iMagicNumber != SMS_MAGIC)
		return (SMS_NSMS);

	/* read size of of header */
	if (fread ((void *) &iHeadBSize, (size_t) sizeof(int), (size_t)1, 
		*ppSmsFile) < (size_t)1)
		return (SMS_RDERR);
	
	if (iHeadBSize <= 0)
		return (SMS_RDERR);
     
  /* read number of data Records */
  if (fread ((void *) &nRecords, (size_t) sizeof(int), (size_t)1, 
	         *ppSmsFile) < (size_t)1)
		return (SMS_RDERR);

	if (nRecords <= 0)
		return (SMS_RDERR);
	
  /* read size of data Records */
	if (fread ((void *) &iRecordBSize, (size_t) sizeof(int), (size_t)1, 
	           *ppSmsFile) < (size_t)1)
		return (SMS_RDERR);

	if (iRecordBSize <= 0)
		return (SMS_RDERR);

	/* allocate memory for header */
	if (((*ppSmsHeader) = (SMSHeader *)malloc (iHeadBSize)) == NULL)
		return (SMS_MALLOC);

	/* read header */
	rewind (*ppSmsFile);
	if (fread ((void *) (*ppSmsHeader), 1, iHeadBSize, *ppSmsFile) < iHeadBSize)
		return (SMS_RDERR);

	/* set pointers to variable part of header */
	if ((*ppSmsHeader)->nLoopRecords > 0)
		(*ppSmsHeader)->pILoopRecords = (int *) ((char *)(*ppSmsHeader) + 
			sizeof(SMSHeader));
						
	if ((*ppSmsHeader)->nSpecEnvelopePoints > 0)
		(*ppSmsHeader)->pFSpectralEnvelope = 
			(float *) ((char *)(*ppSmsHeader) + sizeof(SMSHeader) + 
			           sizeof(int) * (*ppSmsHeader)->nLoopRecords);
			
	if ((*ppSmsHeader)->nTextCharacters > 0)
		(*ppSmsHeader)->pChTextCharacters = 
			(char *) ((char *)(*ppSmsHeader) + sizeof(SMSHeader) + 
			sizeof(int) * (*ppSmsHeader)->nLoopRecords +
			sizeof(float) * (*ppSmsHeader)->nSpecEnvelopePoints);

	return (SMS_OK);			
}

I will admit that I am not sure why a double pointer is used, but that is how the code was handed to me. I'm not sure I understand what you wrote about modifying the local variable; the local variable is a pointer to the structure.

thanks for the help,
Rich