SQLite

** The pager is used to access a database disk file.  It implements
** atomic commit and rollback through the use of a journal file that
** is separate from the database file.  The pager also implements file
** locking to prevent two processes from writing the same database
** file simultaneously, or one process from reading the database while
** another is writing.
**
** @(#) $Id: pager.c,v 1.596 2009/06/19 00:33:32 drh Exp $
*/
#ifndef SQLITE_OMIT_DISKIO
#include "sqliteInt.h"

/*
** Macros for troubleshooting.  Normally turned off
*/

**
*************************************************************************
** This file contains code used for creating, destroying, and populating
** a VDBE (or an "sqlite3_stmt" as it is known to the outside world.)  Prior
** to version 2.8.7, all this code was combined into the vdbe.c source file.
** But that file was getting too big so this subroutines were split out.
**
** $Id: vdbeaux.c,v 1.461 2009/06/19 00:33:32 drh Exp $
*/
#include "sqliteInt.h"
#include "vdbeInt.h"



/*

** return the most recently inserted opcode.
**
** If a memory allocation error has occurred prior to the calling of this
** routine, then a pointer to a dummy VdbeOp will be returned.  That opcode
** is readable and writable, but it has no effect.  The return of a dummy
** opcode allows the call to continue functioning after a OOM fault without
** having to check to see if the return from this routine is a valid pointer.
**
** About the #ifdef SQLITE_OMIT_TRACE:  Normally, this routine is never called
** unless p->nOp>0.  This is because in the absense of SQLITE_OMIT_TRACE,
** an OP_Trace instruction is always inserted by sqlite3VdbeGet() as soon as
** a new VDBE is created.  So we are free to set addr to p->nOp-1 without
** having to double-check to make sure that the result is non-negative. But
** if SQLITE_OMIT_TRACE is defined, the OP_Trace is omitted and we do need to
** check the value of p->nOp-1 before continuing.
*/
VdbeOp *sqlite3VdbeGetOp(Vdbe *p, int addr){
  static VdbeOp dummy;
  assert( p->magic==VDBE_MAGIC_INIT );
  if( addr<0 ){
#ifdef SQLITE_OMIT_TRACE
    if( p->nOp==0 ) return &dummy;
#endif
    addr = p->nOp - 1;
  }
  assert( (addr>=0 && addr<p->nOp) || p->db->mallocFailed );
  if( p->db->mallocFailed ){
    return &dummy;
  }else{
    return &p->aOp[addr];
  }
}