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。
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。
該例程打開一個指向 SQLite 數據庫文件的連接,返回一個用於其他 SQLite 程序的數據庫連接對象。
如果 filename 參數是 NULL 或 ':memory:',那麼 sqlite3_open() 將會在 RAM 中創建一個內存數據庫,這只會在 session 的有效時間內持續。
如果文件名 filename 不為 NULL,那麼 sqlite3_open() 將使用這個參數值嘗試打開數據庫文件。如果該名稱的文件不存在,sqlite3_open() 將創建一個新的命名為該名稱的數據庫文件並打開。
2sqlite3_exec(sqlite3*, const char *sql, sqlite_callback, void *data, char **errmsg)該例程提供了一個執行 SQL 命令的快捷方式,SQL 命令由 sql 參數提供,可以由多個 SQL 命令組成。
在這裡,第一個參數 sqlite3 是打開的數據庫對象,sqlite_callback 是一個回調,data 作為其第一個參數,errmsg 將被返回用來獲取程序生成的任何錯誤。
sqlite3_exec() 程序解析並執行由 sql 參數所給的每個命令,直到字符串結束或者遇到錯誤為止。
3sqlite3_close(sqlite3*)該例程關閉之前調用 sqlite3_open() 打開的數據庫連接。所有與連接相關的語句都應在連接關閉之前完成。
如果還有查詢沒有完成,sqlite3_close() 將返回 SQLITE_BUSY 禁止關閉的錯誤消息。
下面的 C 代碼段顯示了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
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
下面的 C 代碼段顯示了如何在上面創建的 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
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 代碼段顯示了如何從前面創建的 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
下面的 C 代碼段顯示了如何使用 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
下面的 C 代碼段顯示了如何使用 DELETE 語句刪除任何記錄,然後從 COMPANY 表中獲取並顯示剩余的記錄:
#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