askyb.com » Linux

C++ PostgreSQL Example in Linux

askyb — Thu, 26 Apr 2012 05:37:03 +0000

In this tutorial, i’ll demonstrate an example on how to connect to PostgreSQL database using gcc in linux. Also, i’ll demonstrate some basic SQL execution in the C++ example so that it give better understading to you how all of these are working. If you are looking a tutorial for windows platform, you could visit the following link which demonstrate the tutorial for windows platform. C++ PostgreSQL Example in Windows To begin this tutorial, let’s make sure that you have the PostgreSQL install into your linux box. I’m using Ubuntu linux in this demo. Use the following command to download & intstall PostgreSQL if it’s not exists in your linux box.

$ sudo apt-get install postgresql

Let’s turn on the psql command console with the following command:

$ sudo -u postgres psql template1

Let’s create a password for this by using the following command in psql console:

# \password postgres

You will need to key in you password now. I use password “test123″ in this demo. Let’s create the database now by using the following command in psql console. Our database name in this demo called “testdb”.

# create database testdb;

At this point, we’ve the PostgreSQL database created and we can now writing some C++ code to establish connection to this database. We will start the coding part in our cpp file now. I called the cpp file – “PSQLTest.cpp”. Make sure that you include the following header accordingly. libpq-fe.h must be included.

1
2
3
4

#include
#include "libpq-fe.h"

using namespace std;

Now we start our very first functon named CloseConn(). This function will make sure that we close the database connection accordingly.

1
2
3
4
5
6

/* Close connection to database */
void CloseConn(PGconn *conn)
{
PQfinish(conn);
getchar();
}

Next, we create a function named ConnectDB(). This function will establish a connection to PostgreSQL server. Please be sure that you provide the correct parameters in PostgreSQL(). Prior to this example, i have setup a database called testdb with user password of test123 during the installation. You might need to modify it accordingly in order to make sure the compilation success.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19

/* Establish connection to database */
PGconn *ConnectDB()
{
PGconn *conn = NULL;

// Make a connection to the database
conn = PQconnectdb("user=postgres password=test123 dbname=testdb hostaddr=127.0.0.1 port=5432");

// Check to see that the backend connection was successfully made
if (PQstatus(conn) != CONNECTION_OK)
{
cout << "Connection to database failed.\n";
CloseConn(conn);
}

cout << "Connection to database - OK\n";

return conn;
}

Next, we create a function named CreateEmployeeTable(). This function will create an employee table in our testdb database.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18

/* Create employee table */
void CreateEmployeeTable(PGconn *conn)
{
// Execute with sql statement
PGresult *res = PQexec(conn, "CREATE TABLE employee (Fname char(30), Lname char(30))");

if (PQresultStatus(res) != PGRES_COMMAND_OK)
{
cout << "Create employee table failed\n";
PQclear(res);
CloseConn(conn);
}

cout << "Create employee table - OK\n";

// Clear result
PQclear(res);
}

Next, we create a function named InsertEmployeeRec(). This function will take 2 parameters, fname and lname in char pointer type, to form a SQL statement. It then will be executed in order to store the record into the employee table.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26

/* Append SQL statement and insert record into employee table */
void InsertEmployeeRec(PGconn *conn, const char * fname, const char * lname)
{
// Append the SQL statment
std::string sSQL;
sSQL.append("INSERT INTO employee VALUES ('");
sSQL.append(fname);
sSQL.append("', '");
sSQL.append(lname);
sSQL.append("')");

// Execute with sql statement
PGresult *res = PQexec(conn, sSQL.c_str());

if (PQresultStatus(res) != PGRES_COMMAND_OK)
{
cout << "Insert employee record failed\n";
PQclear(res);
CloseConn(conn);
}

cout << "Insert employee record - OK\n";

// Clear result
PQclear(res);
}

Next, we create a function named FetchEmployeeRec(). This function will fetch all the record in employee table and display it on the console windows.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70

/* Fetch employee record and display it on screen */
void FetchEmployeeRec(PGconn *conn)
{
// Will hold the number of field in employee table
int nFields;

// Start a transaction block
PGresult *res = PQexec(conn, "BEGIN");

if (PQresultStatus(res) != PGRES_COMMAND_OK)
{
cout << "BEGIN command failed\n";
PQclear(res);
CloseConn(conn);
}

// Clear result
PQclear(res);

// Fetch rows from employee table
res = PQexec(conn, "DECLARE emprec CURSOR FOR select * from employee");
if (PQresultStatus(res) != PGRES_COMMAND_OK)
{
cout << "DECLARE CURSOR failed\n";
PQclear(res);
CloseConn(conn);
}

// Clear result
PQclear(res);

res = PQexec(conn, "FETCH ALL in emprec");

if (PQresultStatus(res) != PGRES_TUPLES_OK)
{
cout << "FETCH ALL failed\n";
PQclear(res);
CloseConn(conn);
}

// Get the field name
nFields = PQnfields(res);

// Prepare the header with employee table field name
cout << "\nFetch employee record:";
cout << "\n********************************************************************\n";
for (int i = 0; i < nFields; i++)
printf("%-30s", PQfname(res, i));
cout << "\n********************************************************************\n";

// Next, print out the employee record for each row
for (int i = 0; i < PQntuples(res); i++)
{
for (int j = 0; j < nFields; j++)
printf("%-30s", PQgetvalue(res, i, j));
printf("\n");
}

PQclear(res);

// Close the emprec
res = PQexec(conn, "CLOSE emprec");
PQclear(res);

// End the transaction
res = PQexec(conn, "END");

// Clear result
PQclear(res);
}

Next, we create a function named RemoveAllEmployeeRec(). This function will remove all record in employee table.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18

/* Erase all record in employee table */
void RemoveAllEmployeeRec(PGconn *conn)
{
// Execute with sql statement
PGresult *res = PQexec(conn, "DELETE FROM employee");

if (PQresultStatus(res) != PGRES_COMMAND_OK)
{
cout << "Delete employees record failed.\n";
PQclear(res);
CloseConn(conn);
}

cout << "\nDelete employees record - OK\n";

// Clear result
PQclear(res);
}

Next, we create a function named DropEmployeeTable(). This function will drop or remove the employee from the testdb database.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18

/* Drop employee table from the database*/
void DropEmployeeTable(PGconn *conn)
{
// Execute with sql statement
PGresult *res = PQexec(conn, "DROP TABLE employee");

if (PQresultStatus(res) != PGRES_COMMAND_OK)
{
cout << "Drop employee table failed.\n";
PQclear(res);
CloseConn(conn);
}

cout << "Drop employee table - OK\n";

// Clear result
PQclear(res);
}

Finally, we update the main entry point function so that it call all the functions that we have created to demonstrate what we intend to show in this example.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25

int main()
{
PGconn *conn = NULL;

conn = ConnectDB();

if (conn != NULL)
{
CreateEmployeeTable(conn);
InsertEmployeeRec(conn, "Mario", "Hewardt");
InsertEmployeeRec(conn, "Daniel", "Pravat");
FetchEmployeeRec(conn);

cout << "\nPress ENTER to remove all records & table.....\n";
getchar();

RemoveAllEmployeeRec(conn);

DropEmployeeTable(conn);

CloseConn(conn);
}

return 0;
}

Try to compile and run the application now. You should see the following screenshot. REMEMBER, in order to make sure that the compilation can be done successfully, you must tell the gcc compiler where to find postgres include file. Also, you must include postgres library into your c++ project as well. All this can be done by supplying the following argument in the gcc command. If you are new to C++ compilation in Linux, please visit to my previous post which should guide you on how to compile C++ in Linux. Compiling C++ code by using g++ in Ubuntu

$ g++ PSQLTest.cpp -I /usr/include/postgresql/include -l pq -o PSQLTest
$ ./PSQLTest

If you try to break the C++ program before it remove and drop the employee table. Enter to psql command console and you should be able to read you table data as the following screenshot. Download sample source code: PSQLTest.zip

Connecting Ubuntu Server to Dropbox Account

askyb — Tue, 03 Apr 2012 07:58:34 +0000

I was looking for a solution to share some of my files in my Ubuntu server to others and while thinking of “cloud computing” at that time, I am thinking if i can try to share my files by linking my box to my existing dropbox account or not. Thus, i give a try and it seem it works. Here are the steps how to do it. 1. Download and extract the dropbox client with the following command: For 32-bit:

$ wget -O dropbox.tar.gz "http://www.dropbox.com/download?plat=lnx.x86"

For 64-bit:

$ wget -O dropbox.tar.gz "http://www.dropbox.com/download?plat=lnx.x86_64"

2. Extract the file

tar -xzvf dropbox.tar.gz

3. Run the dropbox client deamon wiht the following command:

$ ~/.dropbox-dist/dropboxd

4. Since the server is not link to any dropbox account yet, so you will see the following message keep showing every few second:

This client is not linked to any account...
Please visit https://www.dropbox.com/cli_link?host_id=ed2986f99681f0a7b0bf1cd36c79d3e9&cl=en_US to link this machine.
This client is not linked to any account...
Please visit https://www.dropbox.com/cli_link?host_id=ed2986f99681f0a7b0bf1cd36c79d3e9&cl=en_US to link this machine.

5. You may now copy & paste the link to any browser by using any computer so that it will start to link this machine to your dropbox account. You will be asking to provide your username & password in order to link this to your dropbox account. 6. Once it’s successful, you will see the the following message in your Ubuntu linux machine:

$ Client successfully linked, Welcome ASKYB!

7. Now you may press CTRL + C to terminate the deamon process now. 8. You can manually start the service by running the following command:

$ ~/.dropbox-dist/dropbox

9. You may start to snyc and copy any file to your dropbox folder now.

C++ SQLite Example in Linux

askyb — Tue, 03 Apr 2012 02:56:28 +0000

This example will demonstrate how you can write a C++ program to utilize SQLite as your program database file in Linux environment. I am using Ubuntu in this demonstration. If you are new to C++ & SQLite in Ubuntu, it is advisable that you read the following article so that you have better understanding what to do before you can compile your c++ program and utilize SQLite in your system. Compiling C++ code by using g++ in Ubuntu Installing SQLite in Ubuntu To start the demo, let’s create a cpp file now and I rename it as SqliteSample.cpp. Also, include the the following header file from sqlite to our demo program.

#include

We now create a new callback function. The callback function is triggered once there is data ready to display. This usually happen when the select statement being executed.

1
2
3
4
5
6
7
8
9
10
11
12

// This is the callback function to display the select data in the table
static int callback(void *NotUsed, int argc, char **argv, char **szColName)
{
for(int i = 0; i < argc; i++)
{
std::cout << szColName[i] << " = " << argv[i] << std::endl;
}

std::cout << "\n";

return 0;
}

In the main function, right after the database being open successfully and before it’s close, we need to insert the following codes into the main function so that our mission in this demonstration can be accomplished.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42

int main()
{
sqlite3 *db;
char *szErrMsg = 0;

// open database
int rc = sqlite3_open("askyb.db", &db);

if(rc)
{
std::cout << "Can't open database\n";
} else {
std::cout << "Open database successfully\n";
}

// prepare our sql statements
const char *pSQL[6];
pSQL[0] = "CREATE TABLE Employee(Firstname varchar(30), Lastname varchar(30), Age smallint)";
pSQL[1] = "INSERT INTO Employee(Firstname, Lastname, Age) VALUES ('Woody', 'Alan', 45)";
pSQL[2] = "INSERT INTO Employee(Firstname, Lastname, Age) VALUES ('Micheal', 'Bay', 38)";
pSQL[3] = "SELECT * FROM Employee";

// execute sql
for(int i = 0; i < 4; i++)
{
rc = sqlite3_exec(db, pSQL[i], callback, 0, &szErrMsg);
if(rc != SQLITE_OK)
{
std::cout << "SQL Error: " << szErrMsg << std::endl;
sqlite3_free(szErrMsg);
break;
}
}

// close database
if(db)
{
sqlite3_close(db);
}

return 0;
}

To compile this program, we will need to link the sqlite3 library along with the program as following:

$ g++ SqliteSample.cpp -l sqlite3 -o SqliteSample

If you compiled and run the C++ program now, you should see a similar screenshot as following. Open the askyb.db file from Sqlite console will show you the data as following: Download sample source code: SQLiteSample.cpp

Installing SQLite in Ubuntu

askyb — Mon, 02 Apr 2012 14:01:45 +0000

Installing SQLite in Ubuntu is pretty simple and all you have to do is using the following command to download and install the package.

$ sudo apt-get install sqlite3 libsqlite3-dev

Once it’s downloaded and installed, type the following command to create a SQLite database file. I called the database file — askyb.db. You should see the following screenshot:

$ sqlite3 askybdb.db

Use the ls command to list the file created and you should obsered that askyb.db was created in the directory.

Compiling C++ code by using g++ in Ubuntu

askyb — Mon, 02 Apr 2012 08:26:29 +0000

This article aim to share a little bit of knowledge on how to compile c++ code by using gcc compiler. In case you never experience how to compile c++ code in linux environment, this article will guide you through install of gcc and compile your very first C++ program in Ubuntu. Here it go the steps: 1. Install Ubuntu build-essential package so that it install gcc compiler into the system. Use the following command to download the package.

$ sudo apt-get install build-essential

2. Create the C++ file. Let’s call the c++ file – “HelloWorld.cpp”. I am using vi to create the following C++ file. You may use your preference editor.

1
2
3
4
5
6
7
8
9

#include

using namespace std;

int main()
{
cout << "Hello World\n";
return 0;
}

3. Once the cpp file is saved and it’s ready to compile now by using g++. Use the following command to compile our very first cpp file now.

$ g++ HelloWorld.cpp -o HelloWorld

4. An executable HelloWorld is produced and ready to be executed by using the following command.

$ ./HelloWorld

5. The output of the executable program is displayed as follow: