SQLite - C/C++接口 API（二）

1、打开数据库

SQLITE_API int sqlite3_open16(
　　const void *filename, /* Database filename (UTF-16) */
　　sqlite3 **ppDb /* OUT: SQLite db handle */
);
SQLITE_API int sqlite3_open_v2(
　　const char *filename, /* Database filename (UTF-8) */
　　sqlite3 **ppDb, /* OUT: SQLite db handle */
　　int flags, /* Flags */
　　const char *zVfs /* Name of VFS module to use */
);

/*
** CAPI3REF: Flags For File Open Operations
**
** These bit values are intended for use in the
** 3rd parameter to the [sqlite3_open_v2()] interface and
** in the 4th parameter to the [sqlite3_vfs.xOpen] method.
*/
#define SQLITE_OPEN_READONLY 0x00000001 /* Ok for sqlite3_open_v2() */
#define SQLITE_OPEN_READWRITE 0x00000002 /* Ok for sqlite3_open_v2() */
#define SQLITE_OPEN_CREATE 0x00000004 /* Ok for sqlite3_open_v2() */
#define SQLITE_OPEN_DELETEONCLOSE 0x00000008 /* VFS only */
#define SQLITE_OPEN_EXCLUSIVE 0x00000010 /* VFS only */
#define SQLITE_OPEN_AUTOPROXY 0x00000020 /* VFS only */
#define SQLITE_OPEN_URI 0x00000040 /* Ok for sqlite3_open_v2() */
#define SQLITE_OPEN_MEMORY 0x00000080 /* Ok for sqlite3_open_v2() */
#define SQLITE_OPEN_MAIN_DB 0x00000100 /* VFS only */
#define SQLITE_OPEN_TEMP_DB 0x00000200 /* VFS only */
#define SQLITE_OPEN_TRANSIENT_DB 0x00000400 /* VFS only */
#define SQLITE_OPEN_MAIN_JOURNAL 0x00000800 /* VFS only */
#define SQLITE_OPEN_TEMP_JOURNAL 0x00001000 /* VFS only */
#define SQLITE_OPEN_SUBJOURNAL 0x00002000 /* VFS only */
#define SQLITE_OPEN_MASTER_JOURNAL 0x00004000 /* VFS only */
#define SQLITE_OPEN_NOMUTEX 0x00008000 /* Ok for sqlite3_open_v2() */
#define SQLITE_OPEN_FULLMUTEX 0x00010000 /* Ok for sqlite3_open_v2() */
#define SQLITE_OPEN_SHAREDCACHE 0x00020000 /* Ok for sqlite3_open_v2() */
#define SQLITE_OPEN_PRIVATECACHE 0x00040000 /* Ok for sqlite3_open_v2() */
#define SQLITE_OPEN_WAL 0x00080000 /* VFS only */

2、sqlite3_prepare函数

SQLITE_API int sqlite3_prepare(
　　sqlite3 *db, /* Database handle */
　　const char *zSql, /* SQL statement, UTF-8 encoded */
　　int nByte, /* Maximum length of zSql in bytes. */
　　sqlite3_stmt **ppStmt, /* OUT: Statement handle */
　　const char **pzTail /* OUT: Pointer to unused portion of zSql */
);
SQLITE_API int sqlite3_prepare_v2(
　　sqlite3 *db, /* Database handle */
　　const char *zSql, /* SQL statement, UTF-8 encoded */
　　int nByte, /* Maximum length of zSql in bytes. */
　　sqlite3_stmt **ppStmt, /* OUT: Statement handle */
　　const char **pzTail /* OUT: Pointer to unused portion of zSql */
);
SQLITE_API int sqlite3_prepare16(
　　sqlite3 *db, /* Database handle */
　　const void *zSql, /* SQL statement, UTF-16 encoded */
　　int nByte, /* Maximum length of zSql in bytes. */
　　sqlite3_stmt **ppStmt, /* OUT: Statement handle */
　　const void **pzTail /* OUT: Pointer to unused portion of zSql */
);
SQLITE_API int sqlite3_prepare16_v2(
　　sqlite3 *db, /* Database handle */
　　const void *zSql, /* SQL statement, UTF-16 encoded */
　　int nByte, /* Maximum length of zSql in bytes. */
　　sqlite3_stmt **ppStmt, /* OUT: Statement handle */
　　const void **pzTail /* OUT: Pointer to unused portion of zSql */
);

3、sqlite3_step

SQLITE_API int sqlite3_step(sqlite3_stmt*);

函数的返回值基于创建sqlite3_stmt参数所使用的函数，假如是使用老版本的接口sqlite3_prepare()和sqlite3_prepare16()，返回值会是 SQLITE_BUSY， SQLITE_DONE， SQLITE_ROW， SQLITE_ERROR 或 SQLITE_MISUSE，

而v2版本的接口sqlite3_prepare_v2()和sqlite3_prepare16_v2()则会同时返回这些结果码和扩展结果码。

4、sqlite3_column

这个过程从执行sqlite3_step()执行一个准备语句得到的结果集的当前行中返回一个列。每次sqlite3_step得到一个结果集的列停下后，

这个过程就可以被多次调用去查询这个行的各列的值。对列操作是有多个函数，均以sqlite3_column为前缀

SQLITE_API const void *sqlite3_column_blob(sqlite3_stmt*, int iCol);

BLOB数据类型是指二进制的数据块，比如要在数据库中存放一张图片，这张图片就会以二进制形式存放，在sqlite中对应的数据类型就是BLOB
SQLITE_API int sqlite3_column_bytes(sqlite3_stmt*, int iCol);
SQLITE_API int sqlite3_column_bytes16(sqlite3_stmt*, int iCol);
SQLITE_API double sqlite3_column_double(sqlite3_stmt*, int iCol);
SQLITE_API int sqlite3_column_int(sqlite3_stmt*, int iCol);
SQLITE_API sqlite3_int64 sqlite3_column_int64(sqlite3_stmt*, int iCol);
SQLITE_API const unsigned char *sqlite3_column_text(sqlite3_stmt*, int iCol);
SQLITE_API const void *sqlite3_column_text16(sqlite3_stmt*, int iCol);
SQLITE_API int sqlite3_column_type(sqlite3_stmt*, int iCol);
SQLITE_API sqlite3_value *sqlite3_column_value(sqlite3_stmt*, int iCol);

5．  sqlite3_finalize

int sqlite3_finalize(sqlite3_stmt *pStmt);

这个过程销毁前面被sqlite3_prepare创建的准备语句，每个准备语句都必须使用这个函数去销毁以防止内存泄露。

编程实例：

 #include <stdio.h>
 #include <string.h>
 #include "../Sqlite3/sqlite3.h"

 int main (int argc, char *argv[])
 {
     char *p_query = "SELECT * FROM PERSON;";
     char *p_name = "mytest.db";
     sqlite3_stmt *p_stmt = NULL;
     char *p_err_msg = NULL;
     int rec = ;
     sqlite3 *p_db = NULL;

     if (SQLITE_OK != (rec = sqlite3_open_v2(p_name, &p_db, SQLITE_OPEN_READONLY, NULL) ))
     {
         printf("sqlite3_open_v2  function err  %s\n");
         return -;
     }

     if (SQLITE_OK != (rec = sqlite3_prepare_v2(p_db, p_query, -, &p_stmt, NULL)))
     {
         printf("sqlite3_prepare_v2  function  err : %s\n", sqlite3_errmsg(p_db));
         sqlite3_close(p_db);
         return -;
     }

     while (SQLITE_ROW == sqlite3_step(p_stmt))
     {
         printf("ID = %d\n", sqlite3_column_int64(p_stmt, ));
         printf("NAME = %s\n", sqlite3_column_text(p_stmt,));
         printf("AGE = %d\n", sqlite3_column_int(p_stmt, ));
         printf("\n");
     }

     sqlite3_close(p_db);
     p_db = NULL;

     return ;
 }

运行结果：