L_ReadFileTag (original) (raw)
Summary
Gets the specified tagged data from a file which supports TIFF tags. Use this function to read any TIFF tag, not just the tags you define.
Syntax
#include "l_bitmap.h"
L_LTFIL_API L_INT L_ReadFileTag(pFile, uTag, pType, pCount, pData, pLoadOptions)
Parameters
L_TCHAR * pFile
Character string containing the input file name.
L_UINT16 uTag
Tag to identify the data. Use the same tag that you specified in the L_SetTag function. Examples of registered tags are:
| Value | Meaning |
|---|---|
| 0x8298 | Copyright comment |
| 0x8769 | General Exif comments |
| 0x8825 | Exif GPS comments |
| 0x80A4 | Annotation TIFF tag defined as ANNTAG_TIFF. |
L_UINT16 * pType
Address of the variable to be updated with the tagged data type. The following values are possible:
| Value | Meaning |
|---|---|
| TAG_BYTE | [1] Byte in the range of 0 to 255. |
| TAG_ASCII | [2] Byte in the range of 0 to 127. |
| TAG_SBYTE | [6] Byte used as a signed number in the range of -128 to +127. |
| TAG_UNDEFINED | [7] Byte in the range of 0 to 255, 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. |
| TAG_IFD | [13] 32-bit IFD offset. |
| TAG_LONG8 | [16] Unsigned 64-bit integer (valid only for BigTIFF formats). |
| TAG_SLONG8 | [17] Signed 64-bit integer (valid only for BigTIFF formats). |
| TAG_IFD8 | [18] 64-bit IFD offset (valid only for BigTIFF formats). |
L_UINT * 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.
L_VOID * pData
Pointer to the buffer to be updated with the data. Pass NULL to use this function's return value to determine the required buffer size.
pLOADFILEOPTION pLoadOptions
Pointer to optional extended load options. Pass NULL to use the default load options.
Returns
| Value | Meaning |
|---|---|
| >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:
- Call the function the first time, specifying NULL in the
pDataparameter. Use the return value to determine the required size of the buffer. - Allocate the buffer.
- Call the function the second time, passing a pointer to your buffer in the pData parameter.
Initially, only TIFF files supported TIFF tags. But the Exif specification provided a mechanism for adding TIFF tags to JPEG files using the APP1 JPEG marker. Additionally, other formats are based on the TIFF specification (CALS, TIFX, KDC) or support Exif metadata (HEIF/HEIC and PNG), so they support TIFF tags. In other words, TIFF tags are supported in file formats other than TIFF. To determine whether a certain file format supports tags, call L_TagsSupported.
For general information about TIFF tags, refer to Implementing TIFF Comments and Tags.
This function will read the data for a tag whose data size is greater than 4 bytes. In certain situations, you might want to read the data offset instead of the data itself. This is useful in order to read tags contained in a MakerNote tag. Use L_ReadFileTags to read the tag's data offset.
If you know the file format, you can speed up the process of reading the tag by passing a FILEINFO structure to the L_ReadFileTag2 function.
To read all the tags in the file call L_ReadFileTags, or call L_EnumFileTags2 to enumerate all the tags in a file.
Required DLLs and Libraries
- LTFIL
- For a listing of the exact DLLs and Libraries needed, based on the toolkit version, refer to Files To Be Included With Your Application.
Platforms
Win32, x64, Linux.
See Also
Functions
- L_ReadFileTag2
- L_ReadFileTags
- L_ReadFileTagMemory
- L_SetTag
- L_GetTag
- L_DeleteTag
- L_TagsSupported
- L_EnumFileTags2
Topics
Example
This example uses L_ReadFileTag to read a tag for the position of a company logo on an image.
It reads the tag from the TIFF file that is created in the example for L_SetTag.
L_INT ReadFileTagExample(L_VOID)
{
L_INT nRet;
L_TCHAR msgbuf[80]; /* buffer for the message string */
L_UINT16 FillOrder = 0x010A; /* Fill Order tag */
L_UINT16 TagType; /* tagged data type */
L_UINT32 TagCount; /* count of data items */
L_VOID * pTagData; /* pointer to the buffer containing the data */
HGLOBAL hBuf; /* handle to the buffer */
L_INT32 BufferSize; /* required size of the buffer */
/* Get the required buffer size */
BufferSize = L_ReadFileTag(MAKE_IMAGE_PATH(TEXT("OCR1.TIF")), FillOrder, &TagType, &TagCount, NULL, NULL);
/* Allocate and lock the buffer */
if ((TagType == TAG_SHORT) && (BufferSize > 0))
{
hBuf = GlobalAlloc(GMEM_MOVEABLE, BufferSize);
pTagData = GlobalLock( hBuf );
}
else
{
return BufferSize;
}
/* Get the tagged data */
nRet = L_ReadFileTag(MAKE_IMAGE_PATH(TEXT("OCR1.TIF")), FillOrder, &TagType, &TagCount, pTagData, NULL);
if(nRet <= 0)
return nRet;
/* Display a message showing the data */
if ((TagType == TAG_SHORT) && (TagCount == 1))
{
wsprintf(msgbuf, TEXT("FillOrder = 0x%02X"), (short)*(L_INT*)pTagData);
MessageBox (NULL, msgbuf, TEXT("Fill Order"), MB_OK);
}
/* Free memory that we no longer need */
GlobalUnlock (hBuf);
GlobalFree(hBuf);
return SUCCESS;
}