SQLite – C/C++
安裝
在C/C++ 程序中使用SQLite 之前,我們需要確保機器上已經有SQLite 庫。 可以查看SQLite 安裝章節了解安裝過程。
C/C++ 接口API
以下是重要的C&C++ / SQLite 接口程序,可以滿足您在C/C++ 程序中使用SQLite 數據庫的需求。 如果您需要了解更多細節,請查看SQLite 官方文檔。
序号 | API & 描述 |
---|---|
1 | sqlite3_open(const char *filename, sqlite3 **ppDb) 该例程打开一个指向 SQLite 数据库文件的连接,返回一个用于其他 SQLite 程序的数据库连接对象。 如果filename参数是 NULL 或 ':memory:',那么 sqlite3_open() 将会在 RAM 中创建一个内存数据库,这只会在 session 的有效时间内持续。 如果文件名 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。如果该名称的文件不存在,sqlite3_open() 将创建一个新的命名为该名称的数据库文件并打开。 |
2 | 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,可以由多个 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作为其第一个参数,errmsg 将被返回用来获取程序生成的任何错误。 sqlite3_exec() 程序解析并执行由sql参数所给的每个命令,直到字符串结束或者遇到错误为止。 |
3 | sqlite3_close(sqlite3*) 该例程关闭之前调用 sqlite3_open() 打开的数据库连接。所有与连接相关的语句都应在连接关闭之前完成。 如果还有查询没有完成,sqlite3_close() 将返回 SQLITE_BUSY 禁止关闭的错误消息。 |
連接數據庫
下面的C 代碼段顯示瞭如何連接到一個現有的數據庫。 如果數據庫不存在,那麼它就會被創建,最後將返回一個數據庫對象。
#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)); exit(0); }else{ fprintf(stderr, "Opened database successfully\n"); } sqlite3_close(db); }
現在,讓我們來編譯和運行上面的程序,在當前目錄中創建我們的數據庫test.db 。 您可以根據需要改變路徑。
$gcc test.c -l sqlite3 $./a.out Opened database successfully
如果要使用C++ 源代碼,可以按照下列所示編譯代碼:
$g++ test.c -l sqlite3
在這裡,把我們的程序鏈接上sqlite3 庫,以便向C 程序提供必要的函數。 這將在您的目錄下創建一個數據庫文件test.db,您將得到如下結果:
-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
創建表
下面的C 代碼段將用於在先前創建的數據庫中創建一個表:
#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; }
上述程序編譯和執行時,它會在test.db 文件中創建COMPANY 表,最終文件列表如下所示:
-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 代碼段顯示瞭如何在上面創建的COMPANY 表中創建記錄:
#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; }
上述程序編譯和執行時,它會在COMPANY 表中創建給定記錄,並會顯示以下兩行:
Opened database successfully Records created successfully
SELECT 操作
在我們開始講解獲取記錄的實例之前,讓我們先了解下回調函數的一些細節,這將在我們的實例使用到。 這個回調提供了一個從SELECT 語句獲得結果的方式。 它聲明如下:
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 */ );
如果上面的回調在sqlite_exec() 程序中作為第三個參數,那麼SQLite 將為SQL 參數內執行的每個SELECT 語句中處理的每個記錄調用這個回調函數。
下面的C 代碼段顯示瞭如何從前面創建的COMPANY 表中獲取並顯示記錄:
#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); 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; }
上述程序編譯和執行時,它會產生以下結果:
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 代碼段顯示瞭如何使用UPDATE 語句來更新任何記錄,然後從COMPANY 表中獲取並顯示更新的記錄:
#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; }
上述程序編譯和執行時,它會產生以下結果:
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 代碼段顯示瞭如何使用DELETE 語句刪除任何記錄,然後從COMPANY 表中獲取並顯示剩餘的記錄:
#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; }
上述程序編譯和執行時,它會產生以下結果:
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