在 C/C++ 程序中使用 SQLite 之前,我們需要確保機(jī)器上已經(jīng)有 SQLite 庫(kù)??梢圆榭?SQLite 安裝章節(jié)了解安裝過(guò)程。
以下是重要的 C&C++ / SQLite 接口程序,可以滿(mǎn)足您在 C/C++ 程序中使用 SQLite 數(shù)據(jù)庫(kù)的需求。如果您需要了解更多細(xì)節(jié),請(qǐng)查看 SQLite 官方文檔。
序號(hào) | API & 描述 |
---|---|
1 | sqlite3_open(const char *filename, sqlite3 *ppDb) 該例程打開(kāi)一個(gè)指向 SQLite 數(shù)據(jù)庫(kù)文件的連接,返回一個(gè)用于其他 SQLite 程序的數(shù)據(jù)庫(kù)連接對(duì)象。 如果 filename 參數(shù)是 NULL 或 ':memory:',那么 sqlite3_open() 將會(huì)在 RAM 中創(chuàng)建一個(gè)內(nèi)存數(shù)據(jù)庫(kù),這只會(huì)在 session 的有效時(shí)間內(nèi)持續(xù)。 如果文件名 filename 不為 NULL,那么 sqlite3_open() 將使用這個(gè)參數(shù)值嘗試打開(kāi)數(shù)據(jù)庫(kù)文件。如果該名稱(chēng)的文件不存在,sqlite3_open() 將創(chuàng)建一個(gè)新的命名為該名稱(chēng)的數(shù)據(jù)庫(kù)文件并打開(kāi)。 |
2 | sqlite3_exec(sqlite3, const char sql, sqlite_callback, void data, char *errmsg) 該例程提供了一個(gè)執(zhí)行 SQL 命令的快捷方式,SQL 命令由 sql 參數(shù)提供,可以由多個(gè) SQL 命令組成。 在這里,第一個(gè)參數(shù) sqlite3 是打開(kāi)的數(shù)據(jù)庫(kù)對(duì)象,sqlite_callback 是一個(gè)回調(diào),data 作為其第一個(gè)參數(shù),errmsg 將被返回用來(lái)獲取程序生成的任何錯(cuò)誤。 sqlite3_exec() 程序解析并執(zhí)行由 sql 參數(shù)所給的每個(gè)命令,直到字符串結(jié)束或者遇到錯(cuò)誤為止。 |
3 | sqlite3_close(sqlite3) 該例程關(guān)閉之前調(diào)用 sqlite3_open() 打開(kāi)的數(shù)據(jù)庫(kù)連接。所有與連接相關(guān)的語(yǔ)句都應(yīng)在連接關(guān)閉之前完成。 如果還有查詢(xún)沒(méi)有完成,sqlite3_close() 將返回 SQLITE_BUSY 禁止關(guān)閉的錯(cuò)誤消息。 |
下面的 C 代碼段顯示了如何連接到一個(gè)現(xiàn)有的數(shù)據(jù)庫(kù)。如果數(shù)據(jù)庫(kù)不存在,那么它就會(huì)被創(chuàng)建,最后將返回一個(gè)數(shù)據(jù)庫(kù)對(duì)象。
#include
#include
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: %sn", sqlite3_errmsg(db));
exit(0);
}else{
fprintf(stderr, "Opened database successfullyn");
}
sqlite3_close(db);
}
現(xiàn)在,讓我們來(lái)編譯和運(yùn)行上面的程序,在當(dāng)前目錄中創(chuàng)建我們的數(shù)據(jù)庫(kù) test.db。您可以根據(jù)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
在這里,把我們的程序鏈接上 sqlite3 庫(kù),以便向 C 程序提供必要的函數(shù)。這將在您的目錄下創(chuàng)建一個(gè)數(shù)據(jù)庫(kù)文件 test.db,您將得到如下結(jié)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 代碼段將用于在先前創(chuàng)建的數(shù)據(jù)庫(kù)中創(chuàng)建一個(gè)表:
#include
#include
#include
static int callback(void *NotUsed, int argc, char **argv, char **azColName){
int i;
for(i=0; i<argc; i++){
printf("%s = %sn", 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: %sn", sqlite3_errmsg(db));
exit(0);
}else{
fprintf(stdout, "Opened database successfullyn");
}
/* 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: %sn", zErrMsg);
sqlite3_free(zErrMsg);
}else{
fprintf(stdout, "Table created successfullyn");
}
sqlite3_close(db);
return 0;
}
上述程序編譯和執(zhí)行時(shí),它會(huì)在 test.db 文件中創(chuàng)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(chuàng)建的 COMPANY 表中創(chuàng)建記錄:
#include
#include
#include
static int callback(void *NotUsed, int argc, char **argv, char **azColName){
int i;
for(i=0; i<argc; i++){
printf("%s = %sn", 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: %sn", sqlite3_errmsg(db));
exit(0);
}else{
fprintf(stderr, "Opened database successfullyn");
}
/* 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: %sn", zErrMsg);
sqlite3_free(zErrMsg);
}else{
fprintf(stdout, "Records created successfullyn");
}
sqlite3_close(db);
return 0;
}
上述程序編譯和執(zhí)行時(shí),它會(huì)在 COMPANY 表中創(chuàng)建給定記錄,并會(huì)顯示以下兩行:
Opened database successfully
Records created successfully
在我們開(kāi)始講解獲取記錄的實(shí)例之前,讓我們先了解下回調(diào)函數(shù)的一些細(xì)節(jié),這將在我們的實(shí)例使用到。這個(gè)回調(diào)提供了一個(gè)從 SELECT 語(yǔ)句獲得結(jié)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(diào)在 sqlite_exec() 程序中作為第三個(gè)參數(shù),那么 SQLite 將為 SQL 參數(shù)內(nèi)執(zhí)行的每個(gè) SELECT 語(yǔ)句中處理的每個(gè)記錄調(diào)用這個(gè)回調(diào)函數(shù)。
下面的 C 代碼段顯示了如何從前面創(chuàng)建的 COMPANY 表中獲取并顯示記錄:
#include
#include
#include
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 = %sn", 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: %sn", sqlite3_errmsg(db));
exit(0);
}else{
fprintf(stderr, "Opened database successfullyn");
}
/* 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: %sn", zErrMsg);
sqlite3_free(zErrMsg);
}else{
fprintf(stdout, "Operation done successfullyn");
}
sqlite3_close(db);
return 0;
}
上述程序編譯和執(zhí)行時(shí),它會(huì)產(chǎn)生以下結(jié)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(yǔ)句來(lái)更新任何記錄,然后從 COMPANY 表中獲取并顯示更新的記錄:
#include
#include
#include
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 = %sn", 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: %sn", sqlite3_errmsg(db));
exit(0);
}else{
fprintf(stderr, "Opened database successfullyn");
}
/* 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: %sn", zErrMsg);
sqlite3_free(zErrMsg);
}else{
fprintf(stdout, "Operation done successfullyn");
}
sqlite3_close(db);
return 0;
}
上述程序編譯和執(zhí)行時(shí),它會(huì)產(chǎn)生以下結(jié)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(yǔ)句刪除任何記錄,然后從 COMPANY 表中獲取并顯示剩余的記錄:
#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(zhí)行時(shí),它會(huì)產(chǎn)生以下結(jié)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