SQL using C/C++ and SQLite

In this article, we’d like to introduce the article about SQLITE combined with C++ or C.
Before we go on with this tutorial, we need to follow the SQLITE3 installation procedure that can be easily found here. At the same time it is required a basic knowledge of SQL.

We will show the following operations:

• Database Connection/Creation
• Create Table
• Insert
• Delete
• Select

For the sake of simplicity, let’s use a simple database made of just one table.

Database Connection/Creation of Table

In this snippet, we will use two routines contained in sqlite3.h library.

- sqlite3_open(const char *filename, sqlite3 **ppDb)
- sqlite3_close(sqlite3 *ppDb)

The Compiling is executed by the add of command -l sqlite3 .

#include <iostream>
#include <sqlite3.h>

int main(int argc, char** argv)
{
    sqlite3* DB;
    int exit = 0;
    exit = sqlite3_open("example.db", &DB);

    if (exit) {
        std::cerr << "Error open DB " << sqlite3_errmsg(DB) << std::endl;
        return (-1);
    }
    else
        std::cout << "Opened Database Successfully!" << std::endl;
    sqlite3_close(DB);
    return (0);
}

Output:

$ g++ createDB.cpp -l sqlite3
$ ./a.out

Opened Database Successfully!

$ ls
create.cpp
a.out
example.db

The first routine returns an integer: if the integer is equal to 0, it succeeded. If the database doesn’t exist yet, it is going to be created in the same directory where the process was executed.
The second one just closes the connection previously opened by SQLITE3_OPEN().
All prepared statement associated with the connection should be finalized prior to closing the connection.

Create Table

In this snippet we will use the routine:

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

#include <iostream>
#include <sqlite3.h>

int main(int argc, char** argv)
{
    sqlite3* DB;
    std::string sql = "CREATE TABLE PERSON("
                      "ID INT PRIMARY KEY     NOT NULL, "
                      "NAME           TEXT    NOT NULL, "
                      "SURNAME          TEXT     NOT NULL, "
                      "AGE            INT     NOT NULL, "
                      "ADDRESS        CHAR(50), "
                      "SALARY         REAL );";
    int exit = 0;
    exit = sqlite3_open("example.db", &DB);
    char* messaggeError;
    exit = sqlite3_exec(DB, sql.c_str(), NULL, 0, &messaggeError);

    if (exit != SQLITE_OK) {
        std::cerr << "Error Create Table" << std::endl;
        sqlite3_free(messaggeError);
    }
    else
        std::cout << "Table created Successfully" << std::endl;
    sqlite3_close(DB);
    return (0);
}

Output:

$ g++ createTable.cpp -l sqlite3
$ ./a.out

Table created Successfully

This routine returns an integer: if the integer is equal to the SQLITE_OK macro, everything worked well.
For this example, the controls about open of Database are omitted, that are written in the past code.

Insert and Delete

We will use the SQLITE3_EXEC() routine for Insert as well. Procedure and checks are similar to the previous one. There is just one difference in the string that we use with the SQLITE3_EXEC().

#include <iostream>
#include <sqlite3.h>
#include <string>

using namespace std;

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* messaggeError;
    int exit = sqlite3_open("example.db", &DB);
    string query = "SELECT * FROM PERSON;";

    cout << "STATE OF TABLE BEFORE INSERT" << endl;

    sqlite3_exec(DB, query.c_str(), callback, NULL, NULL);

    string sql("INSERT INTO PERSON VALUES(1, 'STEVE', 'GATES', 30, 'PALO ALTO', 1000.0);"
               "INSERT INTO PERSON VALUES(2, 'BILL', 'ALLEN', 20, 'SEATTLE', 300.22);"
               "INSERT INTO PERSON VALUES(3, 'PAUL', 'JOBS', 24, 'SEATTLE', 9900.0);");

    exit = sqlite3_exec(DB, sql.c_str(), NULL, 0, &messaggeError);
    if (exit != SQLITE_OK) {
        std::cerr << "Error Insert" << std::endl;
        sqlite3_free(messaggeError);
    }
    else
        std::cout << "Records created Successfully!" << std::endl;

    cout << "STATE OF TABLE AFTER INSERT" << endl;

    sqlite3_exec(DB, query.c_str(), callback, NULL, NULL);

    sql = "DELETE FROM PERSON WHERE ID = 2;";
    exit = sqlite3_exec(DB, sql.c_str(), NULL, 0, &messaggeError);
    if (exit != SQLITE_OK) {
        std::cerr << "Error DELETE" << std::endl;
        sqlite3_free(messaggeError);
    }
    else
        std::cout << "Record deleted Successfully!" << std::endl;

    cout << "STATE OF TABLE AFTER DELETE OF ELEMENT" << endl;
    sqlite3_exec(DB, query.c_str(), callback, NULL, NULL);

    sqlite3_close(DB);
    return (0);
}

Output:

$ g++ insertDelete.cpp -l sqlite3
$ ./a.out
STATE OF TABLE BEFORE INSERT
Records created Successfully!
STATE OF TABLE AFTER INSERT
ID = 1
NAME = STEVE
SURNAME = GATES
AGE = 30
ADDRESS = PALO ALTO
SALARY = 1000.0

ID = 2
NAME = BILL
SURNAME = ALLEN
AGE = 20
ADDRESS = SEATTLE
SALARY = 300.22

ID = 3
NAME = PAUL
SURNAME = JOBS
AGE = 24
ADDRESS = SEATTLE
SALARY = 9900.0

Record deleted Successfully!
STATE OF TABLE AFTER DELETE OF ELEMENT
ID = 1
NAME = STEVE
SURNAME = GATES
AGE = 30
ADDRESS = PALO ALTO
SALARY = 1000.0

ID = 3
NAME = PAUL
SURNAME = JOBS
AGE = 24
ADDRESS = SEATTLE
SALARY = 9900.0

Select

Before we go on showing the Select operation, that we might just as easily consider the most important of all the tutorial, let’s have a look at the Callback prototype, that we are going to use in our example.
This operation lets us to get an output from the Select operation:

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 */
);

Now, we will use the Callback function into the Select as shown in the next snippet:

#include <iostream>
#include <sqlite3.h>

using namespace std;

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;
    int exit = 0;
    exit = sqlite3_open("example.db", &DB);
    string data("CALLBACK FUNCTION");

    string sql("SELECT * FROM PERSON;");
    if (exit) {
        std::cerr << "Error open DB " << sqlite3_errmsg(DB) << std::endl;
        return (-1);
    }
    else
        std::cout << "Opened Database Successfully!" << std::endl;

    int rc = sqlite3_exec(DB, sql.c_str(), callback, (void*)data.c_str(), NULL);

    if (rc != SQLITE_OK)
        cerr << "Error SELECT" << endl;
    else {
        cout << "Operation OK!" << endl;
    }

    sqlite3_close(DB);
    return (0);
}

Output:
$ g++ select.cpp -l sqlite3
$ ./a.out

Opened Database Successfully!
RESULT OF SELECT
ID = 1
NAME = STEVE
SURNAME = GATES
AGE = 30
ADDRESS = PALO ALTO
SALARY = 1000.0

ID = 3
NAME = PAUL
SURNAME = JOBS
AGE = 24
ADDRESS = SEATTLE
SALARY = 9900.0

Operation OK!

This article provides a quick guide to Databases with SQLITE3 using C++/C.
In our examples, we used C++, but when we passed our strings, we called the c_str() method, in order to convert the string in a character array: this proves that all the routines utilised can be utilised in C as well.

This article was written in collaboration with Vittorio Triassi student of Department of Science and Technology University of Naples Parthenope.