The typedef is to shorten the naming of some types e.g. is you want to have short unsigned called SHORTUN for quicker typing you can use the type definition syntax of
typedef <old type> <new type> |
so regarding the example of short unsigned to SHORTUN
typedef short unsigned SHORTUN |
a probably better example would be if you wanted to have a apple as a type (which would be a integer value) then you could
typedef in APPLE |
now you could use the code
APPLE apple = 1; |
Within the standard ubuntu or the derviertives (kubuntu/edubuntu etc) the root password is not set and the way to gain access to the root commands is via the command line
sudo command here |
I personally prefer to have root password set because then I can use the root admin rights on the desktop without having to constantly type in sudo all of the time, so to set the root password to something that I will use you can use this
sudo set password root |
this will set the password to something that you can remember and thus any time that you want to have a console open as root just type in
su |
and then the password and you are in the root console 🙂
Mysql is a database, and to gain access to the data within C++ you will need to be able to “talk” to the database via queries (just like on the mysql command line interface e.g. select * from tablename), the connection process is very similar to the command line interface you will need to supply connection details as in hostname (localhost normally), username, password, database to use and also there are other details that you can pass e.g port number more information can be gained from the MYSQL API pages
To start with I created a struct that will hold the username, host etc details.
struct connection_details { char *server; char *user; char *password; char *database; }; |
In essence to connect to a database I have created a function that will connect and return a MYSQL pointer to the new connection using the structure above connection_details.
MYSQL* mysql_connection_setup(struct connection_details mysql_details) { // first of all create a mysql instance and initialize the variables within MYSQL *connection = mysql_init(NULL); // connect to the database with the details attached. if (!mysql_real_connect(connection,mysql_details.server, mysql_details.user, mysql_details.password, mysql_details.database, 0, NULL, 0)) { printf("Conection error : %s\n", mysql_error(connection)); exit(1); } return connection; } |
That is it, you are connected now, now you can perform some sql queries, once again I have created a function to accomplish this and it returns a MYSQL_RES (mysql result pointer)
MYSQL_RES* mysql_perform_query(MYSQL *connection, char *sql_query) { // send the query to the database if (mysql_query(connection, sql_query)) { printf("MySQL query error : %s\n", mysql_error(connection)); exit(1); } return mysql_use_result(connection); } |
since you are now connected and also preformed a query, lets say the query was
SHOW TABLES; |
You can traverse the results with a while loop in C++ and use the mysql_fetch_row function from within the mysql library set where a row is a type of MYSQL_ROW.
MYSQL_ROW row; while ((row = mysql_fetch_row(res)) !=NULL) printf("%s\n", row[0]); |
Here is the full code that will display all of the tables within the mysql database database, you will need to alter the username and password for the mysql access details.
#include <mysql.h> #include <stdio.h> #include <stdlib.h> // just going to input the general details and not the port numbers struct connection_details { char *server; char *user; char *password; char *database; }; MYSQL* mysql_connection_setup(struct connection_details mysql_details) { // first of all create a mysql instance and initialize the variables within MYSQL *connection = mysql_init(NULL); // connect to the database with the details attached. if (!mysql_real_connect(connection,mysql_details.server, mysql_details.user, mysql_details.password, mysql_details.database, 0, NULL, 0)) { printf("Conection error : %s\n", mysql_error(connection)); exit(1); } return connection; } MYSQL_RES* mysql_perform_query(MYSQL *connection, char *sql_query) { // send the query to the database if (mysql_query(connection, sql_query)) { printf("MySQL query error : %s\n", mysql_error(connection)); exit(1); } return mysql_use_result(connection); } int main() { MYSQL *conn; // the connection MYSQL_RES *res; // the results MYSQL_ROW row; // the results row (line by line) struct connection_details mysqlD; mysqlD.server = "localhost"; // where the mysql database is mysqlD.user = "mysqlusername"; // the root user of mysql mysqlD.password = "mysqlpassword"; // the password of the root user in mysql mysqlD.database = "mysql"; // the databse to pick // connect to the mysql database conn = mysql_connection_setup(mysqlD); // assign the results return to the MYSQL_RES pointer res = mysql_perform_query(conn, "show tables"); printf("MySQL Tables in mysql database:\n"); while ((row = mysql_fetch_row(res)) !=NULL) printf("%s\n", row[0]); /* clean up the database result set */ mysql_free_result(res); /* clean up the database link */ mysql_close(conn); return 0; } |
To compile up this program you will need to link to the mysql libraries and headers that are used within the program, e.g. mysql.h at the top of the program. To gain access to these, there is a nice mysql_config (you may need to install it via your package manager system if you do not have it already).
Here are my outputs of what is required on the command line for the g++ compiler
mysql_config --cflags -I/usr/include/mysql -DBIG_JOINS=1 -fno-strict-aliasing -DUNIV_LINUX mysql_config --libs -Wl,-Bsymbolic-functions -rdynamic -L/usr/lib/mysql -lmysqlclient |
These are the g++/c++ switches that tell the compiler where the libraries (-L) are and the headers (-I) and to insert into the g++/c++ compiler line within linux you can do something like
g++ -o mysqlconnect $(mysql_config --cflags) mysqlconnect.cpp $(mysql_config --libs) |
Where the mysqlconnect.cpp is the c++ file of the above program and the output would be
./mysqlconnect MySQL Tables in mysql database: columns_priv db event func general_log help_category help_keyword help_relation help_topic host ndb_binlog_index plugin proc procs_priv servers slow_log tables_priv time_zone time_zone_leap_second time_zone_name time_zone_transition time_zone_transition_type user |
In Object oriented programming languages, there is a nice keyword that is “new” what this does is create a new instance of a object and run the objects constructor method and setup up the internal variables, for example.
class classA { private int x; public classA() { x= 0;} public classA(int value) { x = value;} } ... classA a = new classA(); |
this will create a new instance of A with the constructor (same name as the class) setting x equal to 0. What is happening is that the variable “a” is pointing to a memory location of the newly created object on the memory heap for example.
Local variables
| Object | Memory location / value |
| a | 0x0102 |
which the 0x0102 memory location is pointing to a newly constructed classA space
| Memory location | Object | values |
| 0x0102 | classA – a instance | over head (garage collection etc) |
| 0x0104 | x value | 0 |
There is over head details associated with the classA (a instance) for the garage collection/polymorphism for example. So the actual “a” variable is just pointing to this place in memory, if you created a new classA instance then another place in memory will be created, for example lets create classA a2 as
classA a2 = new classA(); |
and now a example of the memory locations / values would be similar to
Local variables
| Object | Memory location / value |
| a | 0x0102 |
| a2 | 0x0108 |
with the memory heap as such.
| Memory location | Object | values |
| 0x0102 | classA – a instance | over head (garage collection etc) |
| 0x0104 | x value | 0 |
| 0x0108 | classA – a2 instance | over head (garage collection etc) |
| 0x010a | x value | 0 |
so you would have thought that if you did,
if (a == a2) |
then they would be equal, since both have a value of 0 ? well this is not the case, since the == is just comparing the value within the variable and thus the a = 0x0102 and a2 = 0x0108 which are not equal. To compare two different instances of a class you need to override the Equals function within the class (all classes are derived from object class)
So the code would be
// override the inhertant object object Equals function public override bool Equals(object obj) { // cast the obj into a classA and then compare the x values if (x == ((classA)obj).x) return true; else return false; } |
and now you can compare the two classA instances with
if (a.Equals(a2)) |
since the Equals function is actually comparing the values within the class instance and not the a/a2 variable values (which point to memory locations).
Here is the full code
using System; namespace equaltest { class classA { private int x; public classA() { x= 0;} public classA(int value) { x = value;} public int xValue { get { return x;} set { x = value;} } // override the inhertant object object Equals function public override bool Equals(object obj) { // cast the obj into a classA and then compare the x values if (x == ((classA)obj).x) return true; else return false; } } class MainClass { public static void Main(string[] args) { classA a = new classA(); a.xValue = 10; Console.WriteLine("A x value = " + a.xValue); classA a2 = new classA(); a2.xValue = 10; Console.WriteLine("A2 x value = " +a2.xValue); //so they are the same in x values, but are they the same !! == if (a == a2) Console.WriteLine("a does equal a2"); else Console.WriteLine("a does not equal a2"); // of course they are NOT the same value, because the equals is comparing there actual object values // and not there x value inside them, and with the "new" keyword they are both pointing to different // places on the heap of storage, thus they are NOT the same.. // a may equal heap storage = 0x1010 // a2 may equal heap storage= 0x1020 // both have the same x value but different memory location values. // but implementing a Eqauls comparsion function you can compare the two variables internals // as you see fit. if (a.Equals(a2)) Console.WriteLine("a does equal a2"); else Console.WriteLine("a does not equal a2"); } } } |
and the output would be
A x value = 10 A2 x value = 10 a does not equal a2 a does equal a2 |
since I am overriding the Equals from the base object class, the compiler may warn that I am not overriding the GetHaseCode(), but that is k for this example.
Example of the compiler warning message
Description=`equaltest.classA' overrides Object.Equals(object) but does not override Object.GetHashCode()(CS0659)] |
With javascript you can do allot of fun things that a static page, in this example I am going to use the getDocumentID to obtain a image (img) HTML tag, and whilst I have this as a javascript object I can then alter the src image details.
I have created a “a” href HTML tag that will not go anywhere, but I am using the onclick javascript method to call the javascript function which references the id name within the img HTML tag.
<a onclick="javascript:alterImg()">Alter Image</a> <img src="pic1.jpg" width="250" height="350" id="imagesrc"/> |
and within the alterImg javascript function, getting the image (img HTML tag) via the ID
function alterImg() { // get the element img into the imgobject variable var imgobject = document.getElementById('imagesrc'); // change the src of the image to the other image to display. imgobject.src = pictureImage; // change the image to the other image. if (pictureImage == "pic2.jpg") pictureImage = "pic1.jpg"; else pictureImage = "pic2.jpg"; } |
Here is the full code and if you save the below as changeimage.html
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> <html> <script language="javascript"> var pictureImage = "pic2.jpg"; function alterImg() { // get the element img into the imgobject variable var imgobject = document.getElementById('imagesrc'); // change the src of the image to the other image to display. imgobject.src = pictureImage; // change the image to the other image. if (pictureImage == "pic2.jpg") pictureImage = "pic1.jpg"; else pictureImage = "pic2.jpg"; } </script> <body onload="alterImagenow()"> <a onclick="javascript:alterImg()">Alter Image</a> <img src="pic1.jpg" width="250" height="350" id="imagesrc"/> </body> </html> |
The output would be this.. click on “Alter Image”.
You can save the images by selecting the image and right clicking save as..
WordPress is a blogging software that runs on a webserver, the great thing about wordpress is that you are able to extend the functions to create the pages/comments/archives etc on the blogging site. You are also able to create your own themes that will use the functions that you can create within that theme So lets it straight, a plugin for the wordpress is the way that you can extend the functional aspects of the whole site that is not dependent on the theme that you using (a theme is what you view on the web page the “style” (css) of the site for example).
There is two main directories within the wordpress directory structure to add in new themes (wp-content/themes) and the plugins (wp-content/plugins) this is where you place the code to extend the basic wordpress install.
In this example I going to extend the action get_header, if you save the code below into the directory wp-content/plugins/codingfriends_helloworld as codingfriends_helloworld.php
<?php /* Plugin Name: Coding friends hello world Plugin URI: http://www.codingfriends.com/ Description: Outputs hello world Version: 0.1 Author: Genux Author URI: http://www.codingfriends.com License: GPL2 */ function codingfriends_helloworld() { echo "hello world"; } add_action('get_header', 'codingfriends_helloworld'); ?> |
once you have saved that file, then goto your wordpress admin page, on the left is the Plugins link, click on that and within there will be the “new” plugin called coding friends hello world, you just need to activate it and then hey presto it works. There will be “hello world” at the top of the wordpress installed pages within the main site (not the wp-admin part of the site).
What is happening is that you have created a function called codingfriends_hellworld, which outputs “hello world”, but the main part is the
add_action |
this will add this function to a defined plugin action (to get a list of all of the actions (these happen within the core site), and filters (alter text within the site, e.g. pages that you add to the site, comments etc) you can use look here).
So when the action get_header is called within the main wordpress application, it will call your new function (codingfriends_helloworld).
There is tons of things that you can do with these, alter the comments when posted back to the site, pages etc, just look at the API list.
Method programming with C++ is a way to save time when you need to redo same/similar code, and also it allows for clearer code because when you read the code you can tell what is happening instead of just having the same code over and over again within the main method of the program.
To declare a method within c++ there is syntax for the way that a method is defined.
[return type] methodname(parameters if required...) |
So for example if you want to pass in two integer variables and then to return a integer variable (the function could add the parameters together so shall we call it addTwoNumbers,
int addTwoNumbers(int value1, int value2); |
this means that the return value is a int (integer), you “call” the method by its name (addTwoNumbers) and pass in local variables to the method in the parameters (value1 and value2).
Here is a full c++ code example that will read in two values from the keyboard and output the result to the screen.
#include <iostream> #include <exception> #include <stdio.h> //using the namespace std (standard) for the cin -> console input using namespace std; int addTwoNumbers(int val1, int val2) { return (val1 + val2); } int main() { // setup the defaul values. int val1 =0, val2 =0; try { // output to the console printf("Please enter number 1 : "); // read in the input, if not a integer value, this will // cause a error cin >> val1; printf("Please enter number 2 : "); cin >> val2; } catch (exception& e) { // write out any error exception printf("Not a valid input %s\n", e.what()); } // output the answer of the two inputted values. printf("Answer : %d\n", addTwoNumbers(val1, val2)); return 0; } |
and here is the output
Please enter number 1 : 20 Please enter number 2 : 10 Answer : 30 |
