C/C++连接SQLite
C/C++连接SQLite
在本章中,您将学习如何在C/C++程序中使用SQLite。
安装
在开始使用SQLite接口之前,您需要确保在机器上设置了SQLite。您可以查看SQLite安装一章来了解安装过程。
C/C++接口APIs
以下是重要的C/C++ SQLite接口,它可以满足您使用C/C++操作SQLite数据库的要求。
API | 说明 |
---|---|
sqlite3_open(const char *filename, sqlite3 **ppDb) | 打开SQLite数据库的连接,并返回一个数据库连接对象,供其他SQLite例程使用。如果filename参数为NULL或':memory:',sqlite3_open()将在RAM中创建一个内存中数据库,该数据库仅在会话期间持续。如果文件名不为空,sqlite3_open()会尝试使用数据库文件的值来打开该文件。如果不存在同名文件,sqlite3_open()将新建一个同名的数据库文件。 |
sqlite3_exec(sqlite3*, const char *sql, sqlite_callback, void *data, char **errmsg) | 这个接口提供了一种快速、简单的方法来执行由SQL参数提供的SQL命令,SQL参数可以由多个SQL命令组成。这里,第一个参数SQLite 3是一个开放的数据库对象,SQLite_callback是一个回调,data是它的第一个参数,errmsg将返回异常引发的错误信息。SQLite3_exec()解析并执行SQL参数中给出的每个命令,直到它到达字符串末尾或遇到错误。 |
sqlite3_close(sqlite3*) | 关闭之前通过调用sqlite3_open()打开的数据库连接。在关闭连接之前,所有与连接相关联的语句都应该执行完毕。如果任何查询仍未完成,sqlite3_close()将返回SQLITE_BUSY,错误消息由于语句未完成而无法关闭。 |
连接数据库
下面的C代码段展示了如何连接到现有数据库。如果数据库不存在,那么它将被创建,最后返回一个数据库对象。
#include <stdio.h> #include <sqlite3.h> int main(int argc, char* argv[]) { sqlite3 *db; char *zErrMsg = 0; int rc; rc = sqlite3_open("test.db", &db); if( rc ) { fprintf(stderr, "Can't open database: %s\n", sqlite3_errmsg(db)); return(0); } else { fprintf(stderr, "Opened database successfully\n"); } sqlite3_close(db); }
现在,让我们编译并运行上面的程序,程序在当前目录中创建了数据库test.db。你可以根据要求改变你的文件路径。 $gcc test.c -l sqlite3 $./a.out Opened database successfully
如果您要使用c++,那么您可以按如下方式编译代码
$g++ test.c -l sqlite3
这里,我们将程序与SQLite 3库链接起来,为C程序提供所需的功能。这将在您的目录中创建一个数据库文件test.db,您将得到以下结果。
-rwxr-xr-x. 1 root root 7383 May 8 02:06 a.out -rw-r--r--. 1 root root 323 May 8 02:05 test.c -rw-r--r--. 1 root root 0 May 8 02:06 test.db
创建表
下面的C代码段将在之前创建的数据库中创建一张表:
#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)); return(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; } 当编译并执行上述程序时,它将在你的test.db中创建COMPANY表,文件的最终列表如下所示: -rwxr-xr-x. 1 root root 9567 May 8 02:31 a.out -rw-r--r--. 1 root root 1207 May 8 02:31 test.c -rw-r--r--. 1 root root 3072 May 8 02:31 test.db INSERT操作 下面的C代码段展示了如何在上面创建的COMPANY表中插入记录: #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)); return(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; }
当编译并执行上述程序时,它将在COMPANY表中创建指定的记录:
Opened database successfully Records created successfully
SELECT 操作
在继续示例之前,让我们来看看回调函数的一些细节,我们在示例中使用了回调函数。这个回调提供了一种从SELECT语句中获取结果的方法。它包含以下声明:
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 */ );
如果上述回调作为第三个参数在sqlite_exec()中提供,SQLite将为在SQL参数中执行的每个SELECT语句中处理的每个记录调用这个回调函数。
下面的C代码段展示了如何从COMPANY表中获取和显示记录:
#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)); return(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); 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; }
当编译并执行上述程序时,它将产生以下结果。
Opened database successfully Callback function called: ID = 1 NAME = Paul AGE = 32 ADDRESS = California SALARY = 20000.0 Callback function called: ID = 2 NAME = Allen AGE = 25 ADDRESS = Texas SALARY = 15000.0 Callback function called: ID = 3 NAME = Teddy AGE = 23 ADDRESS = Norway SALARY = 20000.0 Callback function called: ID = 4 NAME = Mark AGE = 25 ADDRESS = Rich-Mond SALARY = 65000.0 Operation done successfully
UPDATE 操作
下面的C代码段展示了如何使用UPDATE语句更新记录,然后从COMPANY表中获取并显示更新的记录。
#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)); return(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; }
当编译并执行上述程序时,它将产生以下结果。
Opened database successfully Callback function called: ID = 1 NAME = Paul AGE = 32 ADDRESS = California SALARY = 25000.0 Callback function called: ID = 2 NAME = Allen AGE = 25 ADDRESS = Texas SALARY = 15000.0 Callback function called: ID = 3 NAME = Teddy AGE = 23 ADDRESS = Norway SALARY = 20000.0 Callback function called: ID = 4 NAME = Mark AGE = 25 ADDRESS = Rich-Mond SALARY = 65000.0 Operation done successfully
DELETE 操作
下面的C代码段展示了如何使用DELETE语句删除记录,然后从COMPANY表中提取并显示剩余的记录。
#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)); return(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; }
当编译并执行上述程序时,它将产生以下结果。
Opened database successfully Callback function called: ID = 1 NAME = Paul AGE = 32 ADDRESS = California SALARY = 20000.0 Callback function called: ID = 3 NAME = Teddy AGE = 23 ADDRESS = Norway SALARY = 20000.0 Callback function called: ID = 4 NAME = Mark AGE = 25 ADDRESS = Rich-Mond SALARY = 65000.0 Operation done successfully