SQLite

  const char *zDbFilename;    /* name of the database file */
  char *zFreeOnClose;         /* Filename to free when closing */
  const char *zVfs;           /* Name of VFS to use */
  sqlite3_stmt *pStmt;   /* Current statement if any. */
  FILE *pLog;            /* Write log output here */
  int *aiIndent;         /* Array of indents used in MODE_Explain */
  int nIndent;           /* Size of array aiIndent[] */
  int iIndent;           /* Index of current op in aiIndent[] */
};

/*
** These are the allowed modes.
*/
#define MODE_Line     0  /* One column per line.  Blank line between records */
#define MODE_Column   1  /* One record per line in neat columns */

        }else{
           w = 10;
        }
        if( p->mode==MODE_Explain && azArg[i] && strlen30(azArg[i])>w ){
          w = strlen30(azArg[i]);
        }
        if( i==1 && p->aiIndent && p->pStmt ){

          if( p->iIndent<p->nIndent ){
            fprintf(p->out, "%*.s", p->aiIndent[p->iIndent], "");
          }
          p->iIndent++;
        }
        if( w<0 ){
          fprintf(p->out,"%*.*s%s",-w,-w,
              azArg[i] ? azArg[i] : p->nullvalue, i==nArg-1 ? "\n": "  ");
        }else{
          fprintf(p->out,"%-*.*s%s",w,w,
              azArg[i] ? azArg[i] : p->nullvalue, i==nArg-1 ? "\n": "  ");

**       and "Goto" by 2 spaces.
*/
static void explain_data_prepare(struct callback_data *p, sqlite3_stmt *pSql){
  const char *zSql;               /* The text of the SQL statement */
  const char *z;                  /* Used to check if this is an EXPLAIN */
  int *abYield = 0;               /* True if op is an OP_Yield */
  int nAlloc = 0;                 /* Allocated size of p->aiIndent[], abYield */
  int iOp;                        /* Index of operation in p->aiIndent[] */

  const char *azNext[] = { "Next", "Prev", "VPrev", "VNext", "SorterNext", 0 };
  const char *azYield[] = { "Yield", "SeekLt", "SeekGt", "RowSetRead", 0 };
  const char *azGoto[] = { "Goto", 0 };

  /* Try to figure out if this is really an EXPLAIN statement. If this
  ** cannot be verified, return early.  */
  zSql = sqlite3_sql(pSql);
  if( zSql==0 ) return;
  for(z=zSql; *z==' ' || *z=='\t' || *z=='\n' || *z=='\f' || *z=='\r'; z++);
  if( sqlite3_strnicmp(z, "explain", 7) ) return;

  for(iOp=0; SQLITE_ROW==sqlite3_step(pSql); iOp++){
    int i;
    int iAddr = sqlite3_column_int(pSql, 0);
    const char *zOp = (const char*)sqlite3_column_text(pSql, 1);

    /* Set p2 to the P2 field of the current opcode. Then, assuming that
    ** p2 is an instruction address, set variable p2op to the index of that
    ** instruction in the aiIndent[] array. p2 and p2op may be different if
    ** the current instruction is part of a sub-program generated by an
    ** SQL trigger or foreign key.  */
    int p2 = sqlite3_column_int(pSql, 3);
    int p2op = (p2 + (iOp-iAddr));

    /* Grow the p->aiIndent array as required */
    if( iOp>=nAlloc ){
      nAlloc += 100;
      p->aiIndent = (int*)sqlite3_realloc(p->aiIndent, nAlloc*sizeof(int));
      abYield = (int*)sqlite3_realloc(abYield, nAlloc*sizeof(int));
    }
    abYield[iOp] = str_in_array(zOp, azYield);
    p->aiIndent[iOp] = 0;
    p->nIndent = iOp+1;

    if( str_in_array(zOp, azNext) ){
      for(i=p2op; i<iOp; i++) p->aiIndent[i] += 2;
    }
    if( str_in_array(zOp, azGoto) && p2op<p->nIndent && abYield[p2op] ){
      for(i=p2op; i<iOp; i++) p->aiIndent[i] += 2;
    }
  }

  p->iIndent = 0;
  sqlite3_free(abYield);
  sqlite3_reset(pSql);
}

/*
** Free the array allocated by explain_data_prepare().
*/
static void explain_data_delete(struct callback_data *p){
  sqlite3_free(p->aiIndent);
  p->aiIndent = 0;
  p->nIndent = 0;
  p->iIndent = 0;
}

/*
** Execute a statement or set of statements.  Print 
** any result rows/columns depending on the current mode 
** set via the supplied callback.
**