SQLite C++接口API

时间  2020-05-22 标签 sqlite c++ 接口 api

SQLite接口

如下是重要的 C&C++ / SQLite 接口程序，能够知足您在 C/C++ 程序中使用 SQLite 数据库的需求。web

  1. sqlite3_open(const char *filename, sqlite3 **ppDb)
    该例程打开一个指向 SQLite 数据库文件的链接，返回一个用于其余 SQLite 程序的数据库链接对象。

若是 filename 参数是 NULL 或 ‘:memory:’，那么 sqlite3_open() 将会在 RAM 中建立一个内存数据库，这只会在 session 的有效时间内持续。sql

若是文件名 filename 不为 NULL，那么 sqlite3_open() 将使用这个参数值尝试打开数据库文件。若是该名称的文件不存在，sqlite3_open() 将建立一个新的命名为该名称的数据库文件并打开。数据库

  1. sqlite3_exec(sqlite3*, const char *sql, sqlite_callback, void *data, char **errmsg)
    该例程提供了一个执行 SQL 命令的快捷方式，SQL 命令由 sql 参数提供，能够由多个 SQL 命令组成。

在这里，第一个参数 sqlite3 是打开的数据库对象，sqlite_callback 是一个回调，data 做为其第一个参数，errmsg 将被返回用来获取程序生成的任何错误。session

sqlite3_exec() 程序解析并执行由 sql 参数所给的每一个命令，直到字符串结束或者遇到错误为止。ide

  1. sqlite3_close(sqlite3*)
    该例程关闭以前调用 sqlite3_open() 打开的数据库链接。全部与链接相关的语句都应在链接关闭以前完成。

若是还有查询没有完成，sqlite3_close() 将返回 SQLITE_BUSY 禁止关闭的错误消息。svg

链接数据库

#include <stdio.h>
#include <sqlite3.h>

//test.c
int main(int argc, char* argv[])
{
   sqlite3 *db;
   char *zErrMsg = 0;
   int rc;

   rc = sqlite3_open("test.db", &db); //链接一个现有的数据库，若是数据库不存在，那么它就会被建立，最后将返回一个数据库对象

   if( rc ){ //若是返回一个数据库对象，说明打开不成功
      fprintf(stderr, "Can't open database: %s\n", sqlite3_errmsg(db));
      exit(0);
   }else{
      fprintf(stderr, "Opened database successfully\n");
   }
   sqlite3_close(db);
}

//在当前目录中建立咱们的数据库 test.db，能够根据须要改变路径，而后执行代码
$g++ test.c -l sqlite3

建立数据库表

#include <stdio.h>
#include <stdlib.h>
#include <sqlite3.h> 

static int callback(void *NotUsed, int argc, char **argv, char **azColName){
   int i;
   for(i=0; i<argc; i++){
      printf("%s = %s\n", azColName[i], argv[i] ? argv[i] : "NULL");
   }
   printf("\n");
   return 0;
}

int main(int argc, char* argv[])
{
   sqlite3 *db;
   char *zErrMsg = 0;
   int  rc;
   char *sql;

   /* Open database */
   rc = sqlite3_open("test.db", &db);
   if( rc ){
      fprintf(stderr, "Can't open database: %s\n", sqlite3_errmsg(db));
      exit(0);
   }else{
      fprintf(stdout, "Opened database successfully\n");
   }

   /* Create SQL statement */
   sql = "CREATE TABLE COMPANY("  \
         "ID INT PRIMARY KEY     NOT NULL," \
         "NAME           TEXT    NOT NULL," \
         "AGE            INT     NOT NULL," \
         "ADDRESS        CHAR(50)," \
         "SALARY         REAL );";

   /* Execute SQL statement */
   rc = sqlite3_exec(db, sql, callback, 0, &zErrMsg);
   if( rc != SQLITE_OK ){
   fprintf(stderr, "SQL error: %s\n", zErrMsg);
      sqlite3_free(zErrMsg);
   }else{
      fprintf(stdout, "Table created successfully\n");
   }

   sqlite3_close(db);
   return 0;
}

Insert操做

#include <stdio.h>
#include <stdlib.h>
#include <sqlite3.h>

static int callback(void *NotUsed, int argc, char **argv, char **azColName){
   int i;
   for(i=0; i<argc; i++){
      printf("%s = %s\n", azColName[i], argv[i] ? argv[i] : "NULL");
   }
   printf("\n");
   return 0;
}

int main(int argc, char* argv[])
{
   sqlite3 *db;
   char *zErrMsg = 0;
   int rc;
   char *sql;

   /* Open database */
   rc = sqlite3_open("test.db", &db);
   if( rc ){
      fprintf(stderr, "Can't open database: %s\n", sqlite3_errmsg(db));
      exit(0);
   }else{
      fprintf(stderr, "Opened database successfully\n");
   }

   /* Create SQL statement */
   sql = "INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) "  \
         "VALUES (1, 'Paul', 32, 'California', 20000.00 ); " \
         "INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) "  \
         "VALUES (2, 'Allen', 25, 'Texas', 15000.00 ); "     \
         "INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY)" \
         "VALUES (3, 'Teddy', 23, 'Norway', 20000.00 );" \
         "INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY)" \
         "VALUES (4, 'Mark', 25, 'Rich-Mond ', 65000.00 );";

   /* Execute SQL statement */
   rc = sqlite3_exec(db, sql, callback, 0, &zErrMsg);
   if( rc != SQLITE_OK ){
      fprintf(stderr, "SQL error: %s\n", zErrMsg);
      sqlite3_free(zErrMsg);
   }else{
      fprintf(stdout, "Records created successfully\n");
   }

   sqlite3_close(db);
   return 0;
}

//程序编译和执行成功，并会显示如下两行：
Opened database successfully
Records created successfully

SELECT 操做

在咱们开始讲解获取记录的实例以前，让咱们先了解下回调函数的一些细节，这将在咱们的实例使用到。这个回调提供了一个从 SELECT 语句得到结果的方式。它声明以下：函数

typedef int (sqlite3_callback)(
void, /* Data provided in the 4th argument of sqlite3_exec() /
int, / The number of columns in row /
char*, /* An array of strings representing fields in the row /
char* /* An array of strings representing column names */
);
若是上面的回调在 sqlite_exec() 程序中做为第三个参数，那么 SQLite 将为 SQL 参数内执行的每一个 SELECT 语句中处理的每一个记录调用这个回调函数。code

#include <stdio.h>
#include <stdlib.h>
#include <sqlite3.h>

static int callback(void *data, int argc, char **argv, char **azColName){
   int i;
   fprintf(stderr, "%s: ", (const char*)data);
   for(i=0; i<argc; i++){
      printf("%s = %s\n", azColName[i], argv[i] ? argv[i] : "NULL");
   }
   printf("\n");
   return 0;
}

int main(int argc, char* argv[])
{
   sqlite3 *db;
   char *zErrMsg = 0;
   int rc;
   char *sql;
   const char* data = "Callback function called";

   /* Open database */
   rc = sqlite3_open("test.db", &db);
   if( rc ){
      fprintf(stderr, "Can't open database: %s\n", sqlite3_errmsg(db));
      exit(0);
   }else{
      fprintf(stderr, "Opened database successfully\n");
   }

   /* Create SQL statement */
   sql = "SELECT * from COMPANY";

   /* Execute SQL statement */
   rc = sqlite3_exec(db, sql, callback, (void*)data, &zErrMsg); //callback做为第三个参数，每一个记录都将调用一次callback
   if( rc != SQLITE_OK ){
      fprintf(stderr, "SQL error: %s\n", zErrMsg);
      sqlite3_free(zErrMsg);
   }else{
      fprintf(stdout, "Operation done successfully\n");
   }

   sqlite3_close(db);
   return 0;
}

UPDATE 操做

#include <stdio.h>
#include <stdlib.h>
#include <sqlite3.h> 

static int callback(void *data, int argc, char **argv, char **azColName){
   int i;
   fprintf(stderr, "%s: ", (const char*)data);
   for(i=0; i<argc; i++){
      printf("%s = %s\n", azColName[i], argv[i] ? argv[i] : "NULL");
   }
   printf("\n");
   return 0;
}

int main(int argc, char* argv[])
{
   sqlite3 *db;
   char *zErrMsg = 0;
   int rc;
   char *sql;
   const char* data = "Callback function called";

   /* Open database */
   rc = sqlite3_open("test.db", &db);
   if( rc ){
      fprintf(stderr, "Can't open database: %s\n", sqlite3_errmsg(db));
      exit(0);
   }else{
      fprintf(stderr, "Opened database successfully\n");
   }

   /* Create merged SQL statement */
   sql = "UPDATE COMPANY set SALARY = 25000.00 where ID=1; " \
         "SELECT * from COMPANY";

   /* Execute SQL statement */
   rc = sqlite3_exec(db, sql, callback, (void*)data, &zErrMsg);
   if( rc != SQLITE_OK ){
      fprintf(stderr, "SQL error: %s\n", zErrMsg);
      sqlite3_free(zErrMsg);
   }else{
      fprintf(stdout, "Operation done successfully\n");
   }

   sqlite3_close(db);
   return 0;
}

DELETE 操做

#include <stdio.h>
#include <stdlib.h>
#include <sqlite3.h> 

static int callback(void *data, int argc, char **argv, char **azColName){
   int i;
   fprintf(stderr, "%s: ", (const char*)data);
   for(i=0; i<argc; i++){
      printf("%s = %s\n", azColName[i], argv[i] ? argv[i] : "NULL");
   }
   printf("\n");
   return 0;
}

int main(int argc, char* argv[])
{
   sqlite3 *db;
   char *zErrMsg = 0;
   int rc;
   char *sql;
   const char* data = "Callback function called";

   /* Open database */
   rc = sqlite3_open("test.db", &db);
   if( rc ){
      fprintf(stderr, "Can't open database: %s\n", sqlite3_errmsg(db));
      exit(0);
   }else{
      fprintf(stderr, "Opened database successfully\n");
   }

   /* Create merged SQL statement */
   sql = "DELETE from COMPANY where ID=2; " \
         "SELECT * from COMPANY";

   /* Execute SQL statement */
   rc = sqlite3_exec(db, sql, callback, (void*)data, &zErrMsg);
   if( rc != SQLITE_OK ){
      fprintf(stderr, "SQL error: %s\n", zErrMsg);
      sqlite3_free(zErrMsg);
   }else{
      fprintf(stdout, "Operation done successfully\n");
   }
   sqlite3_close(db);
   return 0;
}
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