I really want to inject my C++ program into another (compiled) program. The way I want to do this is changing the first part of bytes (where the program starts) to goto the binary of my program (pasted into an codecave for example) and when it is finished running to goto back where it went before the injected program started running.
Is this is even possible? and if it is, is it a good/smart idea todo so?
Are there other methods of doing so?
For example: I wrote a program that will write the current time to a file and then terminates, so if i inject it to Internet Explorer and launch it, it will first write its current time to a file and then start Internet Explorer.
In order to do this, you should start reading the documentation for PE files, which you can download at microsoft.
Doing this takes a lot research and experimenting, which is beyond the scope of stackoverflow. You should also be aware that doing this depends heavily on the executable you try to patch. It may work with your version, but most likely not with another version. There are also techniques against this kind of attack. May be built into the executable as well as in the OS.
Is it possible?
Yes. Of course, but it's not trivial.
Is it smart?
Depends on what you do with it. Sometimes it may be the only way.