Gliding Phenomena: April 2011

MySQL: Resetting auto-increment value of a table

During development, usually we want to delete records from the table manually, then the tables auto-increment column remains where it was. We might want to reset the auto-increment value for the table.

For example, if you delete records with id's 7,8,9
Now when you insert through application, it inserts the new record starting at 10. But we want it to start at 7.

Use the following SQL to reset to a specific value

 ALTER TABLE my_table AUTO_INCREMENT=7

If you want to delete all records from your table and restart auto-index at 1, then

 TRUNCATE TABLE my_table

MySQL: Calculate DATE, TIME difference in SQL statement using MySQL DB

Following examples showing how to calculated DATE, TIME differences in SQL statement in MySQL database.

Functions used in the following examples are TIMEDIFF and DATEDIFF

 select TIMEDIFF('2011-10-31 12:50:56' , '2011-09-23 12:50:21')   
 The above outputs : 838:59:59

 select TIMEDIFF('15:50:56' , '12:55:21')   
 The above SQL outputs: 02:55:35

 select DATEDIFF('2011-10-31 12:50:56' , '2011-09-23 12:50:21')   
 The above SQL outputs: 38

 select DATEDIFF('2011-10-31' , '2011-09-23')   
 The above SQL outputs: 38

JAVA: Read and Write PPM, PGM images in JAVA

Download the code library from HERE
Also you can download some sample PPM and PGM images from here.

The following helps to setup the project using Eclipse.
This requires 2 Image Processing libraries which are included in the zip. [jai_imageio.jar and clibwrapper_jiio.jar]
If you are not using eclipse, please add these 2 libraries to your project.

After opening Eclipse:

1. Goto File->New->Java Project
2. In the "contents" section, select the radio button "create project from existing source"
3. Click browse to point to the downloaded ImgProcTool folder (Assuming u have unzipped the file)
4. Click Finish on the "new Java Project" window.

TEST IT BY EXECUTING THE PROJECT
A simple sample program IpToolTester.java is included, which reads and writes a sample PGM image.

 public class IpToolTester {  
     public static void main(String[] args) {  
           ImageTool imageTool = new ImageTool();  
           String srcPath = "lena_384.pgm";  
           
           Image srcImg = new Image(srcPath);  
           Image tgtImg = new Image();  
           tgtImg.init(srcImg.getNumRows(), srcImg.getNumCols());  
           imageTool.copyImg(srcImg, tgtImg);  
           tgtImg.save("lena_write.pgm");  
           System.out.println("Done");  
      }  
 }

5. Right click on the project and select "Run as->java application"
6. If everything is fine, there will be console output ending with "Done".
7. Refresh the project, you will see a new .pgm file "lena_write.pgm".

Mac: Installing OOMMF on Mac OS X Snow Leopard 10.6

Mac OS have TCL/TK already installed.
So it is very easy to install OOMMF(Object Oriented MicroMagnetic Framework)

The following steps installs OOMMF at directory ~/apps/oommf12a4pre-20091216

First you need to download the oommf SOURCE code.
Here is the link to download 1.2a4pre snapshots : http://math.nist.gov/~MDonahue/misc/oommf12a4pre-20091216.tar.gz

Once you have downloaded untar to ~/apps/ using the following command in the terminal.
gunzip -c oommf12a4_20040908.tar.gz | tar xvf -

To Install:
Open Terminal and goto to the folder where you untarred.

 $ cd ~/apps/oommf12a4pre-20091216

Run the following 2 commands

 $ tclsh oommf.tcl +platform

The above command prints summary of your platform configuration. Make sure all the config files are located and listed. Example output will be like the following

 oommf.tcl 1.2.0.4 info:  
 OOMMF release 1.2.0.4, snapshot 2009.12.16  
 Platform Name:          darwin  
 Tcl name for OS:     Darwin 10.7.0  
 C++ compiler:          /usr/bin/g++   
 Tcl configuration file:     /usr/lib/tclConfig.sh  
 tclsh:               /usr/bin/tclsh8.5  
 Tcl release:          8.5.7 (config)     8.5.7 (running)  
 Tk configuration file:     /usr/lib/tkConfig.sh  
 wish:               /usr/bin/wish8.5  
 Tk release:          8.5.7 (config)     8.5.7 (running)  
 Tcl threads:          Yes  
 OOMMF threads:          Yes  
  Default thread count:     2

Now you have all the configurations good, to compile and build run the following command

 $ tclsh oommf.tcl pimake

The above command runs for a while. If there is an error, it prints the error on the console.
To launch the application

 $ tclsh oommf.tcl

Mac: Set Up Apache Virtual Hosts on Mac OS X Snow Leopard 10.6

There 3 simple steps to set Up Apache Virtual Hosts on Mac OS X Snow Leopard (10.6.x)
If you dont have time or lazy to follow these 3 simple steps, you can use a script http://code.google.com/p/virtualhost-sh/

Step A:

 1. Open httpd.conf located at /private/etc/apache2/httpd.conf

Open it using "vi" in terminal or open it using "text wrangler". Donot open using any word processing program, they will add unwanted characters into the file.

2. Find the line #Include /private/etc/apache2/extra/httpd-vhosts.conf
Remove the "#" at the beginning.Now it must look like

 # Virtual hosts
Include /private/etc/apache2/extra/httpd-vhosts.conf

Step B:
1. Open httpd-vhosts.conf located at

 /private/etc/apache2/extra/httpd-vhosts.conf

Open it using "vi" in terminal or open it using "text wrangler". Donot open using any word processing program, they will add unwanted characters into the file.

2. There will be 2 existing dummy examples, you could modify one of to suit your needs. For example I modified to as:

 <VirtualHost *:80>  
   DocumentRoot "/Library/WebServer/Documents/mydemo"  
   ServerName mydemo.local  
   ErrorLog "/private/var/log/apache2/mydemo.local-error_log"  
   CustomLog "/private/var/log/apache2/mydemo.local-access_log" common  
 </VirtualHost>

STEP C:

 1. Open hosts located at /private/etc/hosts

Open it using "vi" in terminal or open it using "text wrangler". Donot open using any word processing program, they will add unwanted characters into the file.

2. Add a new line to specify your new virtual host. For example, I added the following line

 127.0.0.1  mydemo.local

Final STEP D:
1. Save all the edited files : httpd.conf, httpd-vhosts.conf, hosts
2. Restart Apache web server: System Preferences > Sharing > Web Sharing, uncheck and check web sharing
3. DONE ! Your virtual host is ready to use.

XML: Simple internal DTD definition example

Best way to validate is using any browser. Open the XML file in any browser.
Also, if you open in Eclipse, you can right click on the .xml file and select "validate".

 <?xml version="1.0"?>  
 <!DOCTYPE notes [  
  <!ELEMENT notes  (note*)>  
  <!ELEMENT note  (to,from,heading,body*)>  
  <!ELEMENT to   (#PCDATA)>  
  <!ELEMENT from  (#PCDATA)>  
  <!ELEMENT heading (#PCDATA)>  
  <!ELEMENT body  (#PCDATA)>  
 ]>  
 <notes>  
      <note>  
           <to>Joe</to>  
           <from>Tom</from>  
           <heading>Hello</heading>  
      </note>  
      <note>  
           <to>Bob</to>  
           <from>Joe</from>  
           <heading>Reminder</heading>  
           <body>this is msg</body>  
      </note>  
 </notes>

PHP: startsWith endsWith functions

 
function startsWith($needle, $haystack){  
    return preg_match('/^'.preg_quote($needle)."/", $haystack);  
}  

function endsWith($needle, $haystack){  
    return preg_match("/".preg_quote($needle) .'$/', $haystack);  
}

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