LMemoryFile::ReadTag

#include "ltwrappr.h"

virtual L_INT32 LMemoryFile::ReadTag(LMemoryBuffer, pLTagDataBuffer, uTag, pType, pCount, pLoadFileOption=NULL)

LBuffer& LMemoryBuffer;	/* an LBuffer object */
LBuffer L_FAR * pLTagDataBuffer;	/* pointer to an LBuffer object */
L_UINT16 uTag;	/* tag to identify the data in the TIFF file */
L_UINT16 L_FAR * pType;	/* address of the variable to be updated with the data type */
L_UINT32 L_FAR * pCount;	/* address of the variable to be updated with the count */
pLOADFILEOPTION pLoadFileOption;	/* pointer to optional extended load options */

Gets the specified tagged data from a TIFF file in memory. This function is provided to support TIFF tags that you define.

Parameter	Description
LMemoryBuffer	A LEAD LBuffer object that contains the file in memory.
pLTagDataBuffer	Pointer to the buffer to be updated with the data. You can pass NULL if you want to use this function's return value to determine the required buffer size.
uTag	Tag to identify the data in the TIFF file. Use the same tag that you specified in the LFileSettings::SetTag function.
pType	Address of the variable to be updated with the tagged data type. Possible values are:
Value	Meaning
TAG_BYTE	[1] Byte.
TAG_ASCII	[2] Byte in the range of 0 to 255.
TAG_SBYTE	[6] Byte used as signed number in the range of -128 to +127.
TAG_UNDEFINED	[7] Byte, with application-defined usage.
TAG_SHORT	[3] Two bytes, unsigned.
TAG_SSHORT	[8] Two bytes, signed.
TAG_LONG	[4] Four bytes, unsigned.
TAG_SLONG	[9] Four bytes, signed.
TAG_RATIONAL	[5] Eight bytes, used as a pair of unsigned long integers, where the first number is the numerator and the second is the denominator of a fraction.
TAG_SRATIONAL	[10] Eight bytes, used as a pair of signed long integers, where the first number is the numerator and the second is the denominator of a fraction.
TAG_FLOAT	[11] Four bytes used as a floating point number.
TAG_DOUBLE	[12] Eight bytes used as a double-precision floating point number.
pCount	Address of the variable to be updated with the count of data items. The count is based on the tagged data type. For example, if the count is 2 and the data type is TAG_DOUBLE, the required buffer size is 16.
pLoadFileOption	Pointer to optional extended load options. Pass NULL to use the default load options.

Returns

>= 0	Length of the tagged data, in bytes.
< 0	An error occurred. Refer to Return Codes.

Comments

It is often convenient to call this function twice, as follows:

1.	Call the function the first time, specifying NULL in the pLTagDataBuffer parameter, and using the return value to determine the required size of the buffer.
2.	Allocate the buffer.
3.	Call the function the second time, passing a pointer to your buffer in the pLTagDataBuffer parameter.

For general information about TIFF tags, refer to Implementing TIFF Comments and Tags.

The LMemoryBuffer parameter is passed by reference, and is a required parameter.

Required DLLs and Libraries

LTFIL
File format DLLs

For a listing of the exact DLLs and Libraries needed, based on the toolkit version, refer to Files To Be Included With Your Application.

See Also

Functions:	LFile::DeleteTag, Class Members
Topics:	Implementing TIFF Comments and Tags

Example

L_VOID TestReadTagMem()
{
   LMemoryFile LeadMemFile ;
   LBuffer LeadMemBuffer ;
   LBuffer LeadCommBuffer ;
   LFile LeadFile ;
   LBitmapBase LeadBitmap;
   L_UINT16 LogoPosition = 0x8001; // my private tags
   L_UINT16 TagType = TAG_SSHORT; // tagged data type
   L_UINT32 TagCount = 4; // count of data items
   L_INT32 BufferSize ;

   L_INT TagData[] = {5, 5, 24, 37,};
   L_VOID L_FAR *pTagData = &TagData; // pointer to the buffer containing tagged data

   LeadFile.SetBitmap(&LeadBitmap) ;
   LeadFile.SetFileName(TEXT("1.tif")) ;

   LeadFile.LoadBitmap() ;

   // Set the tag data to be saved
   LFileSettings::SetTag(LogoPosition, TagType, TagCount, pTagData);

   LeadMemFile.SetBitmap(&LeadBitmap) ;
   LeadMemFile.SaveBitmap(&LeadMemBuffer,FILE_LEAD,24,QS) ;

   // Get the required size of the buffer for the tagged data
   BufferSize = LeadMemFile.ReadTag(LeadMemBuffer, NULL, LogoPosition,
&TagType, &TagCount, NULL);

   if ((TagType != TAG_SSHORT) || (BufferSize < 0))
      return ;
   else
      // Allocate the buffer
      LeadCommBuffer.Reallocate(BufferSize);

   // Get the tagged data
   BufferSize = LeadMemFile.ReadTag(LeadMemBuffer, &LeadCommBuffer, LogoPosition,
&TagType, &TagCount);

   if (BufferSize >= 0)
   MessageBox(NULL, TEXT("ReadTag successful"), TEXT("TAG Memory"),MB_OK) ;
}