Two Simple Lines for Self-Repairing Apps

Introduction

Ever wondered how MS Office 2000 repairs itself if any files are corrupted or missing? Just two lines of code can add this feature to your app.

First off, you must create an installer program from Windows Installer (free for Visual Studio 6.0 or VC++ 6.0 customers). The self-repairing services are provided via the Windows Installer system. If you are not developing for Windows 2000 only, make sure to set the project settings so that the Setup.exe file will install Windows Installer on the system if it is not already present (Windows Installer comes with Windows 2000, but is not included with previous versions of Windows).

Once your program is installed, it can verify and reinstall needed components with the following two lines.

MsiSetInternalUI(INSTALLUILEVEL_NONE,NULL);
MsiReinstallProduct("{A5A0D1C0-DF1A-11D3-99DC-00A0CCFFFAA1}",
       REINSTALLMODE_FILEVERIFY | REINSTALLMODE_FILEMISSING 
       | REINSTALLMODE_FILEOLDERVERSION | REINSTALLMODE_REPAIR);

To compile, you will need to link your product with the installer library (msi.lib) and include the installer header msi.h.

Make sure to replace the product ID with the product ID that is in the settings dialog for your program. This is needed by Windows Installer. Additionally, the first line is not required. However, it will hide the GUI from the user (without it, a Windows installer dialog will appear). Other settings are:

// Authored user interface with wizards, progress, and errors.
NSTALLUILEVEL_FULL
// Authored user interface with wizard dialog boxes suppressed.
INSTALLUILEVEL_REDUCED
// Simple progress and error handling.
INSTALLUILEVEL_BASIC
// The installer chooses an appropriate user interface level.
INSTALLUILEVEL_DEFAULT
// The installation level is not changed.
INSTALLUILEVEL_NOCHANGE
// Completely silent installation.
INSTALLUILEVEL_NONE

For the reinstall function, possible options are:

// Repair any defects encountered.
REINSTALLMODE_REPAIR
// Reinstall only if the file is missing.
REINSTALLMODE_FILEMISSING
// Reinstall if the file is missing or is an older version.
REINSTALLMODE_FILEOLDERVERSION
// Reinstall if the file is missing or is an equal or older version.
REINSTALLMODE_FILEEQUALVERSION
// Reinstall if the file is missing or is not an exact version.
REINSTALLMODE_FILEEXACT
// Check sum executables, and reinstall if they are missing or corrupt.
REINSTALLMODE_FILEVERIFY
// Reinstall all the files regardless of version.
REINSTALLMODE_FILEREPLACE
// Ensure required user regular entries.
REINSTALLMODE_USERDATA
// Ensure required machine regular entries.
REINSTALLMODE_MACHINEDATA
// Validate shortcuts and progman items.
REINSTALLMODE_SHORTCUT

That's it!