LFile::ReadTag

#include "ltwrappr.h"

virtual L_INT LFile::ReadTag(uTag, pType, pCount, pLBuffer, pLoadFileOption=NULL)

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 */
LBuffer L_FAR * pLBuffer;	/* Pointer to the buffer to be updated with the data */
pLOADFILEOPTION pLoadFileOption;	/* pointer to optional extended load options */

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

Parameter	Description
uTag	Tag to identify the data in the TIFF file. Use the same tag that you specified in the LFileSettings::SetTag function. Examples of registered tags are:
	0x8298	Copyright comment
	0x8769	General Exif comments
	0x8825	Exif GPS comments
	0x80A4	Annotation TIFF tag defined as ANNTAG_TIFF.
pType	Address of the variable to be updated with the tagged data type. The following are possible values:
	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.
pLBuffer	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.
pLoadFileOption	Pointer to optional extended load options. Pass NULL to use the default load options.

Returns

SUCCESS	The function was successful.
< 1	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 pData 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 pData parameter.

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

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 TestReadTag()
{
   L_UINT16 LogoPosition = 0x8001; // my private tag
   L_UINT16 TagType; // tagged data type
   L_UINT32 TagCount; // count of data items
   L_INT32 BufferSize; // required size of the buffer
   LFile LeadFile;
   LBuffer LeadBuffer;

   LeadFile.SetFileName(TEXT("1.tif"));

   // Get the required buffer size
   BufferSize = LeadFile.ReadTag( LogoPosition, &TagType, &TagCount, NULL);

   // Allocate and lock the buffer
   if ((TagType == TAG_SSHORT) && (BufferSize > 0))
      LeadBuffer.Reallocate(BufferSize);
   else
      return;

   // Get the tagged data
   LeadFile.ReadTag( LogoPosition, &TagType, &TagCount, &LeadBuffer);
}