Porting Applications from Qt 3 to Qt 4

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The large-scale application usually consists of many libraries and some executable modules.

To reduce time-to-market the following approach looks attractive:

  1. Port the application using Q3Support module. Get it up and running
  2. In the continues way remove Q3Support classes, replace them with Qt4 equivalents and get benefits from all Qt4 improvements


  1. Check library dependencies and order them for "one-pass" build. Probably, it is already done in your Qt3 build environment
  2. Start from the library that does not depend on any other, and follow in the build order
  3. Compile the library using Qt3
  4. Create the test application that uses main classes from the library (just display widgets and fill them with data) for Qt3
  5. Port library to Qt4
  6. Port test application to Qt4
  7. Test that the ported application works in the same way as Qt3-based version.
  8. After processing of all libraries start to port and debug the main application.