Code Completion is a very useful feature of programiing, but it often  strikes in VC++ 6.0. If you meet such matter, try the following step:

1. delete *.ncb, *.opt, *.plg and *.clw files from your project directory
2. rebuild your project.

And you often need CTRL+W to generate the class wizard infmation again.

But the above works quite often but not always. For a better experience, you need to try some comercial tools, for example, Visual Assistant.It is a product of Whold Tomato Software and  provides more powerful functions.