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Khóa học miễn phí SQLite – C/C++ nhận dự án làm có lương

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SQLite – C/C++

In this chapter, you will learn how to use SQLite in C/C++ programs.

Installation

Before you start using SQLite in our C/C++ programs, you need to make sure that you have SQLite library set up on the machine. You can check SQLite Installation chapter to understand the installation process.

C/C++ Interface APIs

Following are important C/C++ SQLite interface routines, which can suffice your requirement to work with SQLite database from your C/C++ program. If you are looking for a more sophisticated application, then you can look into SQLite official documentation.

Sr.No. API & Description
1

sqlite3_open(const char *filename, sqlite3 **ppDb)

This routine opens a connection to an SQLite database file and returns a database connection object to be used by other SQLite routines.

If the filename argument is NULL or ”:memory:”, sqlite3_open() will create an in-memory database in RAM that lasts only for the duration of the session.

If the filename is not NULL, sqlite3_open() attempts to open the database file by using its value. If no file by that name exists, sqlite3_open() will open a new database file by that name.
2

sqlite3_exec(sqlite3*, const char *sql, sqlite_callback, void *data, char **errmsg)

This routine provides a quick, easy way to execute SQL commands provided by sql argument which can consist of more than one SQL command.

Here, the first argument sqlite3 is an open database object, sqlite_callback is a call back for which data is the 1st argument and errmsg will be returned to capture any error raised by the routine.

SQLite3_exec() routine parses and executes every command given in the sql argument until it reaches the end of the string or encounters an error.
3

sqlite3_close(sqlite3*)

This routine closes a database connection previously opened by a call to sqlite3_open(). All prepared statements associated with the connection should be finalized prior to closing the connection.

If any queries remain that have not been finalized, sqlite3_close() will return SQLITE_BUSY with the error message Unable to close due to unfinalized statements.

Connect To Database

Following C code segment shows how to connect to an existing database. If the database does not exist, then it will be created and finally a database object will be returned.

#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: %sn", sqlite3_errmsg(db));
      return(0);
   } else {
      fprintf(stderr, "Opened database successfullyn");
   }
   sqlite3_close(db);
}

Now, let”s compile and run the above program to create our database test.db in the current directory. You can change your path as per your requirement.

$gcc test.c -l sqlite3
$./a.out
Opened database successfully

If you are going to use C++ source code, then you can compile your code as follows −

$g++ test.c -l sqlite3

Here, we are linking our program with sqlite3 library to provide required functions to C program. This will create a database file test.db in your directory and you will have the following result.

-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

Create a Table

Following C code segment will be used to create a table in the previously created database −

#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 = %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));
      return(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;
}

When the above program is compiled and executed, it will create COMPANY table in your test.db and the final listing of the file will be as follows −

-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 Operation

Following C code segment shows how you can create records in COMPANY table created in the above example −

#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 = %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));
      return(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;
}

When the above program is compiled and executed, it will create the given records in COMPANY table and will display the following two lines −

Opened database successfully
Records created successfully

SELECT Operation

Before proceeding with actual example to fetch records, let us look at some detail about the callback function, which we are using in our examples. This callback provides a way to obtain results from SELECT statements. It has the following declaration −

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 */
);

If the above callback is provided in sqlite_exec() routine as the third argument, SQLite will call this callback function for each record processed in each SELECT statement executed within the SQL argument.

Following C code segment shows how you can fetch and display records from the COMPANY table created in the above example −

#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 = %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));
      return(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;
}

When the above program is compiled and executed, it will produce the following result.

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 Operation

Following C code segment shows how we can use UPDATE statement to update any record and then fetch and display updated records from the COMPANY table.

#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 = %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));
      return(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;
}

When the above program is compiled and executed, it will produce the following result.

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 Operation

Following C code segment shows how you can use DELETE statement to delete any record and then fetch and display the remaining records from the COMPANY table.

#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 = %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));
      return(0);
   } else {
      fprintf(stderr, "Opened database successfullyn");
   }

   /* 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: %sn", zErrMsg);
      sqlite3_free(zErrMsg);
   } else {
      fprintf(stdout, "Operation done successfullyn");
   }
   sqlite3_close(db);
   return 0;
}

When the above program is compiled and executed, it will produce the following result.

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

Khóa học lập trình tại Toidayhoc vừa học vừa làm dự án vừa nhận lương: Khóa học lập trình nhận lương tại trung tâm Toidayhoc

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