The autoincrement feature in mysql allows us to create numeric fields that automatically increment by 1 for every row inserted. It does it atomically so we don’t have to worry about any duplicates or collision. However, there are situations when we need an autoincrement field to reset at regular intervals like every month or so…. Read More »
If a file is to be saved in at path /var/www/a/b/c/d/abc.zip where the directory c and d dont exist then the directories have to created. Here is a function that uses recursion to check for directories in a path and create them if they do not exist : /** Make a nested path , creating… Read More »
Box2d Box2d is a 2d physics simulation library written for C++ and ported to many languages including Javascript. From Box2d’s Website Box2D is a feature rich 2D rigid body physics engine, written in C++ by Erin Catto. It has been used in many games, including Crayon Physics Deluxe, winner of the 2008 Independant Game Festival… Read More »
DNS Query Code in C A dns query lets you to lookup the various dns records for a given hostname or domain name on the internet. The simplest use case is to lookup the ip address of a domain name. When you open a url in your browser, it first performs a dns query to… Read More »
PHP’s session_start method stores the session data in files by default. These files are stored in the tmp directory of the OS and are cleared at intervals by the garbage collector. Alternatively the session data can be stored in database as well. Storing session data in database has certain advantages : 1. Limit the number… Read More »
Php from command line PHP scripts are usually opened in a web browser. But they can be run from command line or terminal as well. The syntax to run a script from commandline is very much similar to python or perl. php /path/to/script/index.php Inside a script it might be necessary to test if it is… Read More »
Racing car in box2d Box2d is a physics 2d simulation library and is used in game development. Apart from C/C++ it has ports for various languages like python, javascript etc. With the availability of the html5 canvas element and many other html5 apis, it becomes possible to write browser based games in javascript. So in… Read More »
Resizing images Web applications often need to work with images like pictures of users or photos etc. So the need to resize images comes up when creating thumbnails for example or compressing images for storage. The default library to handle image operations in php is GD. It can be used to resize images. GD vs… Read More »
The php_flag directive can be used to set options that are specific to the php interpreter, directly from the .htaccess file. It is a good way to setup parameters across entire site, without having to repeat them in each php script or code. The following code, turns off the register globals setting in php. <IfModule… Read More »
System load System load is a measure of how busy the system is running the processes. Higher system load simply means more processes are running and more are waiting to be run. When coding php applications, it sometimes is useful or necessary to find the current load on the server/system. For example if you want… Read More »
Path Info Urls When using path info data , the urls of codeignitor apps or your custom mvc frameworks looks something like this example.com/index.php/controller/method/param1/param2 or example.com/controller/method/param1/param2 The path info data can be used to specify which class and method should be invoked on server application. Forward slash in parameter Sometimes it might so happen that… Read More »
The PATH-INFO is the extra path data that follows the name of a script (or servlet) in the URL. Its different from query string. Here is a classic example: https://www.examples.com/index.php/some/path?a=b Now, over here we are actually invoking the script index.php only. However also providing some path-info data “/some/path”, which is then followed by the query… Read More »
information_schema The following query will list out the foreign keys in mysql. It finds it out from the information_schema database. select concat(table_name, '.', column_name) as 'foreign key', concat(referenced_table_name, '.', referenced_column_name) as 'references' from information_schema.key_column_usage where referenced_table_name is not null; The output is a clean table listing out all foreign keys from all databases +———————–+————-+ |… Read More »
The innodb storage engine supports foreign keys in Mysql. To create foreign keys in phpmyadmin : 1. Convert both tables into innodb, if they are not already. 2. View the structure of the table which will have a foreign key. Make the referencing field an INDEX. 3. Now come back to structure view and click… Read More »
Views and mysqldump A little back I tried to backup a database from my webhost and restore it on my localhost mysql. It had a few views. The import of the sql file seemed to work fine. But on accessing the views in phpmyadmin mysql gave the error : #1449 – There is no 'projects'@'localhost'… Read More »
While creating a table a particular column / field can be made autoincrement as : CREATE TABLE students ( id INTEGER NOT NULL GENERATED ALWAYS AS IDENTITY (START WITH 1, INCREMENT BY 1), name VARCHAR(24) NOT NULL, address VARCHAR(1024), CONSTRAINT primary_key PRIMARY KEY (id) ) ; The value of an autoincrement column increments automatically with… Read More »
To go back to the previous page the superglobal variable $_SERVER can be used. $_SERVER[‘HTTP_REFERER’] has the link to the previous page. So to redirect simply : // Method to go to previous page function goback() { header("Location: {$_SERVER['HTTP_REFERER']}"); exit; } goback();
The numerical system used in India differs from the Western system in terms of the placement of the thousands separator. Example : Number -> 1000000 Indian System -> 10,00,000 (Ten Lakh) Western System -> 1,000,000 (1 Million) While echoing numbers in PHP it is possible to format numbers with such separators using functions like number_format…. Read More »
Raw tcp sockets in C Raw sockets can be used to construct a packet manually inside an application. In normal sockets when any data is send over the network, the kernel of the operating system adds some headers to it like IP header and TCP header. So an application only needs to take care of… Read More »
TCP/IP 3-way handshake is done to establish a connection between a client and a server. The process is : 1. Client –SYN Packet–> Server 2. Server –SYN/ACK Packet –> Client 3. Client –ACK Packet –> Server The above 3 steps are followed to establish a connection between source and destination. SYN Flood DOS attacks involves… Read More »