For your convenience comments on how to use this technology under other conditions are included in this section. The Web page that will be used is named RemoteDebugging.html. It's given in Listing 1. Note that only standard HTML tags constitute a page that's usable with most Web servers these days. If you use a remote server you'll need a special page (or special fields on the page) with a logon ID and password and/or other means of authentication that will be automatically filled out with the required credentials in a way similar to other fields that are used in a form. Please see the details below on how the form will be filled out. Security issues related to authentication are a huge topic that's far beyond the scope of this article. If you are new to security, a good place to start is to google the Internet and read the book on secure coding listed in the resources. You'll get many other security references from it.

The Web page with its needed permissions will be put in the appropriate directory of the Web server. If you use the Apache server that comes with Fedora Core 5 with the standard configuration, the directory will be /var/www/html. You may want to read your Web server documentation on where HTML pages should be put if you use other Web servers in Fedora Core 5 or if you use a remote Web server. In the case of a remote Web server you'll need server administration assistance if you're not allowed to ftp (or otherwise submit) the Web page in question to the server and give it appropriate permissions.

The Perl script that will do the job described above is called RemoteCompilation.pl. It's given in Listing 2. With the standard Apache in Fedora Core 5 it should be put under /var/www/cgi-bin. Note that in this case files that are produced by scripts from /var/www/cgi-bin have an owner named apache that belongs to a group with the same name. You may want to issue the command: chown [your user name goes here]:apache RemoteCompilation.pl after you create the script to be able to edit the script and run it. You must replace [your user name goes here] with your Fedora Core 5 user name. Then you'll have to issue the command: chmod 775 RemoteCompilation.pl (or set up permissions with another appropriate tool like Konqueror). Of course you should have enough authority to run these commands. In case of a remote server (or a server other than the Apache under Fedora Core 5) you'll have to read the documentation to figure out what the name of needed group is. If a remote server is used, you'll likely have to contact server administration to figure out what the appropriate permissions for the script are and how to set it up since security is involved here.

Note that with a remote server, the appropriate code for authentication checking must be used just after print start_html in the script (or implement separate software for this purpose). Only standard Perl constructions are used in the script so it's possible to use the script with almost any current Web server. First, the script checks if a standard output of your compiler exists (in the example it's a file called a.out) and deletes it. The script also deletes an auxiliary file named err.txt that will be described below.

After that it reads the code for debugging from the appropriate parameter and the file name for the code from another parameter and writes the code to the file with this name to the server. Chunks of 512 bytes are used for writing. If host operating system and/or compilers require it, you should then insert a statement for changing the file permissions. The needed compiler will be called by the script using the file in question as well as another special auxiliary file with possible errors called err.txt to which any errors produced by the compiler should be redirected.

In our example Intel Fortran for Linux is used. But the same technology can be applied to any other needed compiler. If you use other compilers you'll have to read the documentation and adjust the script accordingly (particularly the statement that calls the compiler). In our case, redirection is provided by 2>err.txt in the corresponding statement. In case of other compilers figure out from the documentation how to provide the redirection. Note that the script files are written in the directory in which the script is located. In the case of a remote server you have to contact server administration to figure out the appropriate directory. Then the script checks if a.out (the default name for the executable file with this compiler) is produced, which means that the compilation is OK. The check is done using a pipeline of ls and grep. If the compilation is OK, the user will see a corresponding message in the browser. If compilation failed (i.e., a.out isn't produced) the script will read each line from err.txt and display it in the browser. Note that in this case the HTML
tag will be added to the end of the line. With other compilers you may want to use another condition to determine whether or not compilation is OK. The condition can be found by reading the documentation.

The application that calls the browser with the page in question from your XP software development tool is given in Listing 3. The name of the .exe file obtained with the source code in Listing 3 is DebuggingUnderLinux.exe. If you use VS.NET 2005 to compile the source, a System.Windows.Forms reference should be added to the "Console application" type of the project. The DebuggingUnderLinux.exe in our example is placed under C:\G77Start, but you can use any directory. Note that in the example the application calls FireFox from a specific location, but you can easily adjust it to any browser with any needed location. If you use FireFox, it should be closed before the application runs again.

The application is called from the tool by the menu, hot keys, etc. and obtains from the caller 2 parameters: the name of the file that contains the code and the path to the directory where the file is located. Most modern software development tools allow these two parameters to be passed via a customizable configuration (please see the examples below). Consider the following popular software development tools under Windows XP: VS.NET 2005 and Crimson from www.crimsoneditor.com. The example of the configuration to be used with the application from VS.NET 2005 is given in Figure 1 and the one from Crimson is given in Figure 2. As soon as configuration is made you can debug the needed code with these tools simply by clicking the hot keys of your choice (CTRL+3). If you use Crimson select Tools | Debugging under Linux. If you use VS.NET 2005 you can use any name for this command and assign hot keys to it. Note that with a remote server, the URL of the Web page used in the application will be given to you by server administration.

If you use VMware workstation 5 or 5.5 for virtualization and Fedora Core 5 as the guest operating system, the URL can be obtained by the following means. Within the Fedora Core 5 terminal window, issue an ifconfig command. Locate "inet addr" in eth0. It will be part of the url. In this example the part in question is 192.168.227.129 and this value is used in the application. You need to obtain the value in question using ifconfig and adjust the application accordingly.

Please refer to Listing 3 on how to get the URL using the part.

To test of the example of this technology you can use dwhet.f (an application for performance measurement from my Web site at www.myjavaserver.com/~akrivitsky/G77.html. (You may want to read my article in JDJ at http://jdj.sys-con.com/read/83099.htm on the subject.) First use it "as is." You will see a "Complilation OK" message in your browser. Then introduce an error by typing "error" anywhere in the code. You'll see a corresponding error message in the browser.

What We Just Did
This example shows you how by simple and therefore effective means (a Web page, a Perl script, and an application) you can debug Linux or Unix code with Windows XP software development tools. In other words, we can run the compiler under another operating system and get the results back to Windows XP with the proposed technology.

Homework for Manufactures
This example offers a solution that fits the needs of many developers. However, it can be polished further by IDE manufactures and included in their products. Here's how. After obtaining results in the browser one sends the following commands to the browser window: CTRL+A to select all the text in the window, CTRL+C to copy the selection to the clipboard, and ALT+F4 to close the window. See Listing 3 on how to send commands to the browser window. Then you can grab the text from the clipboard to your IDE and deal with it in exactly the same way as output from your native IDE compiler for the convenience of your user. The user will be able to get additional help on errors, and get to the line with the error by clicking the corresponding error message. So by using this approach you can give your IDE additional multi-operating system capabilities.

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