Call external function(from one exe to another)

Question

Lets say the process 1 is the main process and the process 2 is the target process(i can't edit it by the way), i want to be able to call a function from the process 2 in the process 1, anyone have a nice way to do that?I was thinking in inject a dll with exports that calls that function and use GetProcAddress externally...Is that possible?Is that the best way to do it?

Thanks for the time.

Answer 1

The title and body of your question ask two subtly different questions.

Having one executable call a function that's contained in another executable is quite easy, at least if the name of the function in question has been exported. You can use LoadLibrary to load an executable just like you would a DLL, then use GetProcAddress to get the address of the function you want to call, and call it normally. Keep in mind, however, that the function may not work correctly without other initialization that happens before it's called inside its own executable.

Calling a function in the context of another process (not just in another executable) is considerably more work. The basic idea is to have a function that makes the call and (for example) writes a result to some memory shared with the process making the call. You then use CreateRemoteThread to have that function execute in the context of the process containing the function you need to call.

If the target process has been written to support it there are other methods such as COM that are intended to support this type of capability much more cleanly. They're generally preferable if available.