SQLite

** state of the virtual machine.
**
** The "sqlite3_stmt" structure pointer that is returned by sqlite3_prepare()
** is really a pointer to an instance of this structure.
*/
struct Vdbe {
  sqlite3 *db;            /* The database connection that owns this statement */
  Vdbe *pPrev,*pNext;     /* Linked list of VDBEs with the same Vdbe.db */
  Parse *pParse;          /* Parsing context used to create this Vdbe */
  ynVar nVar;             /* Number of entries in aVar[] */
  ynVar nzVar;            /* Number of entries in azVar[] */
  u32 magic;              /* Magic number for sanity checking */
  int nMem;               /* Number of memory locations currently allocated */
  int nCursor;            /* Number of slots in apCsr[] */
  u32 cacheCtr;           /* VdbeCursor row cache generation counter */
  int pc;                 /* The program counter */
  int rc;                 /* Value to return */
  int nChange;            /* Number of db changes made since last reset */
  int iStatement;         /* Statement number (or 0 if has not opened stmt) */
  i64 iCurrentTime;       /* Value of julianday('now') for this statement */
  i64 nFkConstraint;      /* Number of imm. FK constraints this VM */
  i64 nStmtDefCons;       /* Number of def. constraints when stmt started */
  i64 nStmtDefImmCons;    /* Number of def. imm constraints when stmt started */

  /* When allocating a new Vdbe object, all of the fields below should be
  ** initialized to zero or NULL */

  Op *aOp;                /* Space to hold the virtual machine's program */
  Mem *aMem;              /* The memory locations */
  Mem **apArg;            /* Arguments to currently executing user function */
  Mem *aColName;          /* Column names to return */
  Mem *pResultSet;        /* Pointer to an array of results */





  char *zErrMsg;          /* Error message written here */

  VdbeCursor **apCsr;     /* One element of this array for each open cursor */
  Mem *aVar;              /* Values for the OP_Variable opcode. */
  char **azVar;           /* Name of variables */
#ifndef SQLITE_OMIT_TRACE
  i64 startTime;          /* Time when query started - used for profiling */
#endif

  int nOp;                /* Number of instructions in the program */
#ifdef SQLITE_DEBUG
  int rcApp;              /* errcode set by sqlite3_result_error_code() */
#endif
  u16 nResColumn;         /* Number of columns in one row of the result set */
  u8 errorAction;         /* Recovery action to do in case of an error */
  u8 minWriteFileFormat;  /* Minimum file format for writable database files */
  bft expired:1;          /* True if the VM needs to be recompiled */
  bft doingRerun:1;       /* True if rerunning after an auto-reprepare */

  bft explain:2;          /* True if EXPLAIN present on SQL command */
  bft changeCntOn:1;      /* True to update the change-counter */
  bft runOnlyOnce:1;      /* Automatically expire on reset */
  bft usesStmtJournal:1;  /* True if uses a statement journal */
  bft readOnly:1;         /* True for statements that do not write */
  bft bIsReader:1;        /* True for statements that read */
  bft isPrepareV2:1;      /* True if prepared with prepare_v2() */

  yDbMask btreeMask;      /* Bitmask of db->aDb[] entries referenced */
  yDbMask lockMask;       /* Subset of btreeMask that requires a lock */

  u32 aCounter[5];        /* Counters used by sqlite3_stmt_status() */







  char *zSql;             /* Text of the SQL statement that generated this */
  void *pFree;            /* Free this when deleting the vdbe */
  VdbeFrame *pFrame;      /* Parent frame */
  VdbeFrame *pDelFrame;   /* List of frame objects to free on VM reset */
  int nFrame;             /* Number of frames in pFrame list */
  u32 expmask;            /* Binding to these vars invalidates VM */
  SubProgram *pProgram;   /* Linked list of all sub-programs used by VM */
  AuxData *pAuxData;      /* Linked list of auxdata allocations */
#ifdef SQLITE_ENABLE_STMT_SCANSTATUS
  i64 *anExec;            /* Number of times each op has been executed */
  int nScan;              /* Entries in aScan[] */
  ScanStatus *aScan;      /* Scan definitions for sqlite3_stmt_scanstatus() */
#endif
};

/*
** The following are allowed values for Vdbe.magic
*/
#define VDBE_MAGIC_INIT     0x16bceaa5    /* Building a VDBE program */
#define VDBE_MAGIC_RUN      0x2df20da3    /* VDBE is ready to execute */
#define VDBE_MAGIC_HALT     0x319c2973    /* VDBE has completed execution */
#define VDBE_MAGIC_RESET    0x48fa9f76    /* Reset and ready to run again */
#define VDBE_MAGIC_DEAD     0x5606c3c8    /* The VDBE has been deallocated */

/*
** Structure used to store the context required by the 
** sqlite3_preupdate_*() API functions.
*/
struct PreUpdate {
  Vdbe *v;

/*
** Create a new virtual database engine.
*/
Vdbe *sqlite3VdbeCreate(Parse *pParse){
  sqlite3 *db = pParse->db;
  Vdbe *p;
  p = sqlite3DbMallocRaw(db, sizeof(Vdbe) );
  if( p==0 ) return 0;
  memset(&p->aOp, 0, sizeof(Vdbe)-offsetof(Vdbe,aOp));
  p->db = db;
  if( db->pVdbe ){
    db->pVdbe->pPrev = p;
  }
  p->pNext = db->pVdbe;
  p->pPrev = 0;
  db->pVdbe = p;

** running it.
*/
void sqlite3VdbeRewind(Vdbe *p){
#if defined(SQLITE_DEBUG) || defined(VDBE_PROFILE)
  int i;
#endif
  assert( p!=0 );
  assert( p->magic==VDBE_MAGIC_INIT || p->magic==VDBE_MAGIC_RESET );

  /* There should be at least one opcode.
  */
  assert( p->nOp>0 );

  /* Set the magic to VDBE_MAGIC_RUN sooner rather than later. */
  p->magic = VDBE_MAGIC_RUN;

  }while( !db->mallocFailed );

  p->nzVar = pParse->nzVar;
  p->azVar = pParse->azVar;
  pParse->nzVar =  0;
  pParse->azVar = 0;
  p->explain = pParse->explain;
  if( db->mallocFailed ){
    p->nVar = 0;
    p->nCursor = 0;
    p->nMem = 0;
  }else{
    p->nCursor = nCursor;
    p->nVar = (ynVar)nVar;
    initMemArray(p->aVar, nVar, db, MEM_Null);
    p->nMem = nMem;
    initMemArray(p->aMem, nMem, db, MEM_Undefined);
    memset(p->apArg, 0, nArg*sizeof(Mem*));
    memset(p->apCsr, 0, nCursor*sizeof(VdbeCursor*));

        sqlite3VdbePrintOp(out, i, &p->aOp[i]);
      }
      fclose(out);
    }
  }
#endif
  p->iCurrentTime = 0;
  p->magic = VDBE_MAGIC_RESET;
  return p->rc & db->errMask;
}
 
/*
** Clean up and delete a VDBE after execution.  Return an integer which is
** the result code.  Write any error message text into *pzErrMsg.
*/

  releaseMemArray(p->aVar, p->nVar);
  releaseMemArray(p->aColName, p->nResColumn*COLNAME_N);
  for(pSub=p->pProgram; pSub; pSub=pNext){
    pNext = pSub->pNext;
    vdbeFreeOpArray(db, pSub->aOp, pSub->nOp);
    sqlite3DbFree(db, pSub);
  }
  if( p->magic!=VDBE_MAGIC_INIT ){
    for(i=p->nzVar-1; i>=0; i--) sqlite3DbFree(db, p->azVar[i]);
  }
  sqlite3DbFree(db, p->azVar);
  vdbeFreeOpArray(db, p->aOp, p->nOp);
  sqlite3DbFree(db, p->aColName);
  sqlite3DbFree(db, p->zSql);
  sqlite3DbFree(db, p->pFree);
#ifdef SQLITE_ENABLE_STMT_SCANSTATUS
  for(i=0; i<p->nScan; i++){