Simple update check function

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Introduction

Almost all programs that are available today have a feature that checks for software updates using the internet. This is a convenient way for both the user and the developer: You don't have to contact all the users (if you know them...) when a new version is available. And the user can be sure to always have the newest version.

In this article I'd like to focus on small programs (e.g. only 1 executable and no nescessary installation program) and developers who have just a simple web space without the possibility to use scripts (only static web pages). Also this code only shows a web page and does not automatically download or install files.

The basic thing we have to do is very simple: Connect to a web site, ask for the newest version, compare it to the current version, and in case there is an update ask the user to download it. You - as the developer - have to use correct version information in your code and update the internet file whenever an update is available.

Program version

Ever looked at the version block of your code in the resource file? This resource consists of two major blocks: A language-independent information on the top containing file version etc. and some blocks where text information can be stored like the copyright. This code only uses the fixed block (FILEVERSION) at the top of this resource. Please be sure to update this block any time you want to release a new version!

What this class does

The new class CUpdateCheck has 1 main function: download a web site and check for updates! If you don't want to change any behaviour you simply use the class "as is" - that's all (besides adding the language-dependant strings). The class has two helper function GetFileVersion()to get the applications File version and GotoURL() which simply opens a web page in the default browser. I got the code for GotoURL() somewhere on the web, so when you are the author please inform me to put your names to the credits.

Using the code, allow auto-updates

[1]: Add a new menu item to your application and handle it in your CWinApp drived class. This could look like this:

void CMyApp::OnAppCheckupdate()
{
  CUpdateCheck checkUpdate;
  checkUpdate.Check(IDS_UPDATE);
}

where the string IDS_UPDATE is e.g. http://www.mywebsite.xxx/update.txt

In case you want to check automatically for updates each time the user start your application put the lines above in the InitInstance function. Or write the last date you checked for updates to the registry and only check once each week. ....

[2]: Add a few strings to the string table:

IDS_UPDATE_AVAILABLE	You currently use version %u.%u of this program. The newest version %u.%u is available online. Do you want to see more information?
IDS_UPDATE_NO	No Updates available.
IDS_UPDATE_NOCHECK	Unable to check for updates.

[3]: Put a file on your webspace (located as referred in IDS_UPDATE) which has the following syntax:

Major Version|Minor Version|URL for Update page

So when your program has currently the version 1,1,0,0 and you want to offer an update to 3,4,0,0 which is available for download at http://www.mydomain.com/updateinfo.html the file should be

3|4|http://www.mydomain.com/updateinfo.html

Limitations

• The file on your web site has to be less than 512 characters
• Only the two leftmost parts of the version info are used. The lower two numbers are normally used as a "Build number" and have no effect on this class
• No automatic download is offered, the user has to download the files from your site and copy/install them

History

01.11.2003: Initial release