SQLite non-table-valued virtual table example

vtab.c

// gcc -shared vtab.c -o vtab.dll -s -static
// create virtual table t using vtab(4); -- 4 is a column count
#include "sqlite3ext.h"
SQLITE_EXTENSION_INIT1
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>

typedef struct vtab_vtab vtab_vtab;
struct vtab_vtab {
	sqlite3_vtab base;
	int colCount;
};

static int vtabCreate(sqlite3 *db, void *pAux, int argc, const char *const*argv, sqlite3_vtab **ppVtab, char **pzErr);

static int vtabConnect(sqlite3 *db, void *pAux, int argc, const char *const*argv, sqlite3_vtab **ppVtab, char **pzErr) {
	vtab_vtab *pNew;
	
	int colCount = argc >= 4 ? atoi(argv[3]) : 0;
	if (colCount <= 0)
		return SQLITE_ERROR;
		
	char query[255 + colCount * 10];
	sprintf(query, "create table x(");
	for (int i = 0; i < colCount; i++) {
		char colName[255];
		sprintf(colName, "%scol%i", i > 0 ? ", " : "", i);
		strcat(query, colName);
	}
	strcat(query, ")");
		
	int rc = sqlite3_declare_vtab(db, query);
	if (rc == SQLITE_OK) {
		pNew = sqlite3_malloc(sizeof(*pNew));
		*ppVtab = (sqlite3_vtab*)pNew;
		if (pNew == 0) 
			return SQLITE_NOMEM;
			
		memset(pNew, 0, sizeof(*pNew));
		pNew->colCount = colCount;
	}
	
	return rc;
}

static int vtabCreate(sqlite3 *db, void *pAux, int argc, const char *const*argv, sqlite3_vtab **ppVtab, char **pzErr) {
	return vtabConnect(db, pAux, argc, argv, ppVtab, pzErr);
}

static int vtabDisconnect(sqlite3_vtab *pVtab){
	vtab_vtab *p = (vtab_vtab*)pVtab;
	sqlite3_free(p);
	return SQLITE_OK;
}

static int vtabBestIndex(sqlite3_vtab *tab, sqlite3_index_info *pIdxInfo) {
	pIdxInfo->estimatedCost = (double)10;
	pIdxInfo->estimatedRows = 10;
	return SQLITE_OK;
}

typedef struct vtab_cursor vtab_cursor;
struct vtab_cursor {
	sqlite3_vtab_cursor base;  
	sqlite3_int64 iRowid;
	int isEof;
};

static int vtabOpen(sqlite3_vtab *p, sqlite3_vtab_cursor **ppCursor) {
	vtab_cursor *pCur;
	pCur = sqlite3_malloc(sizeof(*pCur));
	if (pCur == 0) 
		return SQLITE_NOMEM;
		
	memset(pCur, 0, sizeof(*pCur));
	*ppCursor = &pCur->base;
	return SQLITE_OK;
}

static int vtabClose(sqlite3_vtab_cursor *cur){
	vtab_cursor *pCur = (vtab_cursor*)cur;
	sqlite3_free(pCur);
	
	return SQLITE_OK;
}

static int vtabNext(sqlite3_vtab_cursor *cur) {
	vtab_cursor *pCur = (vtab_cursor*)cur;
	pCur->iRowid++;
	pCur->isEof = pCur->iRowid > 10;
	return SQLITE_OK;
}

static int vtabColumn(sqlite3_vtab_cursor *cur, sqlite3_context *ctx, int colNo){
	vtab_cursor *pCur = (vtab_cursor*)cur;
	sqlite3_result_int(ctx, pow(10, colNo) + pCur->iRowid);
	return SQLITE_OK;
}

static int vtabEof(sqlite3_vtab_cursor *cur){
	vtab_cursor *pCur = (vtab_cursor*)cur;
	return pCur->iRowid >= 10;
}

static int vtabFilter(sqlite3_vtab_cursor *pVtabCursor, int idxNum, const char *idxStr, int argc, sqlite3_value **argv) {
	vtab_cursor *pCur = (vtab_cursor *)pVtabCursor;
	pCur->iRowid = 1;
	return SQLITE_OK;
}

static int vtabRowid(sqlite3_vtab_cursor *cur, sqlite_int64 *pRowid) {
	vtab_cursor *pCur = (vtab_cursor*)cur;
	*pRowid = pCur->iRowid;
	return SQLITE_OK;
}

static sqlite3_module vtabModule = {
  /* iVersion    */ 0,
  /* xCreate     */ vtabCreate,
  /* xConnect    */ vtabConnect,
  /* xBestIndex  */ vtabBestIndex,
  /* xDisconnect */ vtabDisconnect,
  /* xDestroy    */ vtabDisconnect,
  /* xOpen       */ vtabOpen,
  /* xClose      */ vtabClose,
  /* xFilter     */ vtabFilter,
  /* xNext       */ vtabNext,
  /* xEof        */ vtabEof,
  /* xColumn     */ vtabColumn,
  /* xRowid      */ vtabRowid,
  /* xUpdate     */ 0,
  /* xBegin      */ 0,
  /* xSync       */ 0,
  /* xCommit     */ 0,
  /* xRollback   */ 0,
  /* xFindMethod */ 0,
  /* xRename     */ 0,
  /* xSavepoint  */ 0,
  /* xRelease    */ 0,
  /* xRollbackTo */ 0,
  /* xShadowName */ 0
};

#ifdef _WIN32
__declspec(dllexport)
#endif
int sqlite3_vtab_init(sqlite3 *db, char **pzErrMsg, const sqlite3_api_routines *pApi) {
	SQLITE_EXTENSION_INIT2(pApi);
	return sqlite3_create_module(db, "vtab", &vtabModule, 0);
}