Write and read binary data in VARIANT – Code Library

Write and read binary data in VARIANT

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2006-11-22 Category: Win32/MFC 0 2,898 views

We offen need to store some binary data in the mdb database, thus we have to transefer the data by VARIANT structure.
But how to read from binary data from VARIANT or write to? Here is a solution by safe array of VARRIANT.

BOOL GetBinaryFromVariant(COleVariant & ovData, BYTE ** ppBuf, unsigned long * pcBufLen)
{
BOOL fRetVal = FALSE;
//Binary data is stored in the variant as an array of unsigned char
if(ovData.vt == (VT_ARRAY|VT_UI1)) // (OLE SAFEARRAY)
{
//Retrieve size of array
*pcBufLen = ovData.parray->rgsabound[0].cElements;
*ppBuf = new BYTE[*pcBufLen]; //Allocate a buffer to store the data
if(*ppBuf != NULL)
{
void * pArrayData;
//Obtain safe pointer to the array
SafeArrayAccessData(ovData.parray,&pArrayData);
//Copy the bitmap into our buffer
memcpy(*ppBuf, pArrayData, *pcBufLen); //Unlock the variant data
SafeArrayUnaccessData(ovData.parray);
fRetVal = TRUE;
}
}
return fRetVal;
}



BOOL PutBinaryIntoVariant(COleVariant * ovData, BYTE * pBuf,unsigned long cBufLen)
{
BOOL fRetVal = FALSE;
VARIANT var;
VariantInit(&var); //Initialize our variant
//Set the type to an array of unsigned chars (OLE SAFEARRAY)
var.vt = VT_ARRAY | VT_UI1;
//Set up the bounds structure
SAFEARRAYBOUND rgsabound[1];
rgsabound[0].cElements = cBufLen;
rgsabound[0].lLbound = 0;
//Create an OLE SAFEARRAY
var.parray = SafeArrayCreate(VT_UI1,1,rgsabound);
if(var.parray != NULL)
{
void * pArrayData = NULL;
//Get a safe pointer to the array
SafeArrayAccessData(var.parray,&pArrayData);
//Copy data to it
memcpy(pArrayData, pBuf, cBufLen);
//Unlock the variant data
SafeArrayUnaccessData(var.parray);
*ovData = var;
// Create a COleVariant based on our variant
VariantClear(&var);
fRetVal = TRUE;
}
return fRetVal;
}

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