REDIRECTSEEK Callback Function
#include "l_bitmap.h"
L_SSIZE_T pEXT_CALLBACK YourSeek(nFd, nPos, nOrigin, pUserData)
L_HFILE nFd; |
/* file handle */ |
L_SSIZE_T nPos; |
/* number of bytes to move */ |
L_INT nOrigin; |
/* position to move from */ |
L_VOID* pUserData; |
/* pointer to additional parameters */ |
Replaces the normal LEADTOOLS function for repositioning a file pointer.
Parameter |
Description |
|
nFd |
Identifies the file, using the file handle returned by the REDIRECTOPEN callback function. |
|
nPos |
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 nPos bytes from the beginning of the file. |
|
1 |
Move the file pointer nPos bytes from its current position. |
|
2 |
Move the file pointer nPos 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.
Required DLLs and Libraries
LTKRN For a listing of the exact DLLs and Libraries needed, based on the toolkit version, refer to Files To Be Included With Your Application |
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 *pData; /* Pointer to the buffer. */ L_CHAR *pCurData; /* Current pointer location. */ } USERDATA, * LPUSERDATA; /***************************************************************************************/ L_INT32 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 ((L_INT)(pUserData->pCurData - pUserData->pData)); }