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Function : OS Blocks
OSSwitchBlock - Switch pointer from one memory block to another.

#include <pool.h>
void OSSwitchBlock(

    void far *ptr,
    BLOCKID  thisid,
    BLOCKID  nextid);
Description :

OSSwitchBlock operates on two BLOCKID structures. The first one is UnLocked, and then the second one is Locked. Then the specified pointer is loaded with the memory address associated with the second BLOCKID. This function is actually implemented as a macro. It provides a transparent way for an application to switch between two BLOCKIDs without requiring knowledge of BLOCKID organization.

Note -- this function is actually implemented as a macro: #define OSSwitchBlock(ptr,thisid,nextid) \ { \ if ((thisid).pool != (nextid).pool) \ { \ if ((thisid).pool != NULLHANDLE) \ OSUnlockBlock((thisid)); \ ptr = OSLockBlock(void,(nextid)); \ } \ else \ { \ register char pptr = (char ) &(ptr); \ pptr = pptr + (LONG)((nextid).block - (thisid).block); \ } \ (thisid) = (nextid); \ }

Parameters : Input :

thisid - BLOCKID for the previous block (the one to be unlocked). Note that this BLOCKID is overwritten by the nextid argument; if the user has allocated the block identified by thisid, the BLOCKID must be preserved elsewhere.

nextid - BLOCKID for the new block (the block that will be locked and whose address is to be returned by the routine itself).

Output : (routine) - None.

ptr - Pointer to be loaded with a data pointer associated with the new BLOCKID. Because this function is actually a macro, this argument should be passed in as the pointer itself, rather than a pointer to the pointer. (ex: char far * pData; use pData rather than &pData).

See Also : OSLockBlock OSUnlockBlock