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Comment:Enhance the comments in the templatevtab.c implementation.
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SHA3-256:05f6278a02e5cde89f76ced5af7d508e26576d7291dad7ee9e06b1a3be516cb0
User & Date: drh 2018-04-27 15:17:08
Context
2018-04-27
17:39
Add the ability to use bind parameters in the CLI. The new ".set KEY=VALUE" dot-command works to set bindings. Or use the "-Dkey=value" command-line option. Or use the built-in shell_bindings(k,v) virtual table to set, delete, or changing bindings. check-in: 1f2944d1 user: drh tags: shell-bindings
16:35
Fix a test script error causing tests to fail in soak.test. check-in: 462b52b1 user: dan tags: trunk
15:17
Enhance the comments in the templatevtab.c implementation. check-in: 05f6278a user: drh tags: trunk
2018-04-26
18:34
The previous fix for ticket [d85fffd6ffe856092ed8da] in check-in [0a514e62ad1ebe5c12da8dae] did not completely address the probably in that it only worked for cases where the OP_SCopy that loaded the register was the last instruction in the sequence for the expression, which is not necessarily the case for expressions like CASE...END. This revision prevents the registered that will be recomputed from being cached in the first place. check-in: 9fd0faf5 user: drh tags: trunk
Changes
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Changes to ext/misc/templatevtab.c.

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**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
**
** This file implements a template virtual-table implementation.
** Developers can make a copy of this file as a baseline for writing
** new virtual tables and/or table-valued functions.
**
** Steps for writing a new virtual table implementation:
**
**     (1)  Make a copy of this file.  Prehaps "mynewvtab.c"
**
**     (2)  Replace this header comment with something appropriate for
**          the new virtual table
**
**     (3)  Change every occurrence of "templatevtab" to some other string
**          appropriate for the new virtual table.  Ideally, the new string
**          should be the basename of the source file: "mynewvtab".

**
**     (4)  Run a test compilation to make sure the unmodified virtual
**          table works.
**
**     (5)  Begin making changes to make the new virtual table do what you
**          want it to do.
**
**     (6)  Ensure that all the "FIXME" comments in the file have been dealt
**          with.
**
** This template is minimal, in the sense that it uses only the required
** methods on the sqlite3_module object.  As a result, templatevtab is
** a read-only and eponymous-only table.  Those limitation can be removed
** by adding new methods.






*/
#if !defined(SQLITEINT_H)
#include "sqlite3ext.h"
#endif
SQLITE_EXTENSION_INIT1
#include <string.h>


/* templatevtab_vtab is a subclass of sqlite3_vtab which is
** underlying representation of the virtual table
*/
typedef struct templatevtab_vtab templatevtab_vtab;
struct templatevtab_vtab {
  sqlite3_vtab base;  /* Base class - must be first */
................................................................................
){
  templatevtab_vtab *pNew;
  int rc;

  rc = sqlite3_declare_vtab(db,
           "CREATE TABLE x(a,b)"
       );



  if( rc==SQLITE_OK ){
    pNew = sqlite3_malloc( sizeof(*pNew) );
    *ppVtab = (sqlite3_vtab*)pNew;
    if( pNew==0 ) return SQLITE_NOMEM;
    memset(pNew, 0, sizeof(*pNew));
  }
  return rc;
................................................................................
*/
static int templatevtabColumn(
  sqlite3_vtab_cursor *cur,   /* The cursor */
  sqlite3_context *ctx,       /* First argument to sqlite3_result_...() */
  int i                       /* Which column to return */
){
  templatevtab_cursor *pCur = (templatevtab_cursor*)cur;


  sqlite3_result_int(ctx, (i+1)*1000 + pCur->iRowid);






  return SQLITE_OK;
}

/*
** Return the rowid for the current row.  In this implementation, the
** rowid is the same as the output value.
*/







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**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
**
** This file implements a template virtual-table.
** Developers can make a copy of this file as a baseline for writing
** new virtual tables and/or table-valued functions.
**
** Steps for writing a new virtual table implementation:
**
**     (1)  Make a copy of this file.  Perhaps call it "mynewvtab.c"
**
**     (2)  Replace this header comment with something appropriate for
**          the new virtual table
**
**     (3)  Change every occurrence of "templatevtab" to some other string
**          appropriate for the new virtual table.  Ideally, the new string
**          should be the basename of the source file: "mynewvtab".  Also
**          globally change "TEMPLATEVTAB" to "MYNEWVTAB".
**
**     (4)  Run a test compilation to make sure the unmodified virtual
**          table works.
**
**     (5)  Begin making incremental changes, testing as you go, to evolve
**          the new virtual table to do what you want it to do.



**
** This template is minimal, in the sense that it uses only the required
** methods on the sqlite3_module object.  As a result, templatevtab is
** a read-only and eponymous-only table.  Those limitation can be removed
** by adding new methods.
**
** This template implements an eponymous-only virtual table with a rowid and
** two columns named "a" and "b".  The table as 10 rows with fixed integer
** values. Usage example:
**
**     SELECT rowid, a, b FROM templatevtab;
*/
#if !defined(SQLITEINT_H)
#include "sqlite3ext.h"
#endif
SQLITE_EXTENSION_INIT1
#include <string.h>
#include <assert.h>

/* templatevtab_vtab is a subclass of sqlite3_vtab which is
** underlying representation of the virtual table
*/
typedef struct templatevtab_vtab templatevtab_vtab;
struct templatevtab_vtab {
  sqlite3_vtab base;  /* Base class - must be first */
................................................................................
){
  templatevtab_vtab *pNew;
  int rc;

  rc = sqlite3_declare_vtab(db,
           "CREATE TABLE x(a,b)"
       );
  /* For convenience, define symbolic names for the index to each column. */
#define TEMPLATEVTAB_A  0
#define TEMPLATEVTAB_B  1
  if( rc==SQLITE_OK ){
    pNew = sqlite3_malloc( sizeof(*pNew) );
    *ppVtab = (sqlite3_vtab*)pNew;
    if( pNew==0 ) return SQLITE_NOMEM;
    memset(pNew, 0, sizeof(*pNew));
  }
  return rc;
................................................................................
*/
static int templatevtabColumn(
  sqlite3_vtab_cursor *cur,   /* The cursor */
  sqlite3_context *ctx,       /* First argument to sqlite3_result_...() */
  int i                       /* Which column to return */
){
  templatevtab_cursor *pCur = (templatevtab_cursor*)cur;
  switch( i ){
    case TEMPLATEVTAB_A:
      sqlite3_result_int(ctx, 1000 + pCur->iRowid);
      break;
    default:
      assert( i==TEMPLATEVTAB_B );
      sqlite3_result_int(ctx, 2000 + pCur->iRowid);
      break;
  }
  return SQLITE_OK;
}

/*
** Return the rowid for the current row.  In this implementation, the
** rowid is the same as the output value.
*/