REDIRECTSEEK Callback Function

#include "l_bitmap.h"

L_INT32 L_FAR L_EXPORT YourSeek(FD, lnPos, nOrigin, pUserData)

L_INT FD;	/* file handle */
L_INT32 lnPos;	/* number of bytes to move */
L_INT nOrigin;	/* position to move from */
L_VOID L_FAR *pUserData;	/* pointer to additional parameters */

Replaces the normal LEADTOOLS function for repositioning a file pointer.

Parameter	Description
FD	Identifies the file, using the file handle returned by the REDIRECTOPEN callback function.
lnPos	Specifies the number of bytes the pointer is to be moved.
nOrigin	Specifies the starting position and direction of the pointer. This parameter must be one of the following values:
	Value	Meaning
	0	Move the file pointer lnPos bytes from the beginning of the file.
	1	Move the file pointer lnPos bytes from its current position.
	2	Move the file pointer lnPos bytes from the end of the file.
pUserData	A void pointer that you can use to access a variable or structure containing data that your callback function needs. This gives you a way to receive data indirectly from the function that uses this callback function. (This is the same pointer that you pass in the pUserData parameter of the calling function.)
	Keep in mind that this is a void pointer, which must be cast to the appropriate data type within your callback function.

Returns

>0	The number of bytes that the function wrote to the file.
-1	The function failed.

Comments

For information about using this type of callback, refer to L_RedirectIO.

Example

To see how the following function is defined and called, refer to L_RedirectIO.

/* This procedure is a replacement to the built-in seek procedure.
This emulates the whole seek operation on a memory block, and
adjusts the internal data structures accordingly. */

/************************** Global Declarations **********************************/

typedef struct tagUSERDATA
{
   L_INT32 dwSize;              /* Size of the buffer. /
   L_INT32 dwUsed;              / Number of bytes used. */
   L_CHAR L_HUGE pData;        / Pointer to the buffer. */
   L_CHAR L_HUGE pCurData;     / Current pointer location. */
} USERDATA, L_FAR * LPUSERDATA;
DATA Data;                      /* Pointer to DATA structure */

/***************************************************************************************/
L_INT32 L_FAR L_EXPORT WindowsSeek (L_INT FD, L_INT32 lnPos, L_INT nOrigin, LPUSERDATA pUserData)
{
   UNREFERENCED_PARAMETER (FD);

   switch (nOrigin)
   {
   case 0:                     /* SEEK_SET /
      pUserData->pCurData = pUserData->pData + lnPos;
      pUserData->dwUsed = lnPos;
      break;
   case 1:                     / SEEK_CUR /
      pUserData->pCurData += lnPos;
      pUserData->dwUsed += lnPos;
      break;
   case 2:                     / SEEK_END /
      if (0 <= lnPos)           / Positive value, but at the end, so go to
                                   the end. /
         lnPos = 0;
      else
         lnPos = -(lnPos);      / Seek backwards from the end of the buffer. */
      pUserData->pCurData = pUserData->pData + pUserData->dwSize – lnPos;
      pUserData->dwUsed = pUserData->dwSize – lnPos;
      break;
   }
   return (pUserData->pCurData – pUserData->pData);
}