Question:

  Is there any hope of a decompiler that would convert an executable program
into C/C++ code?

Answer:

  Don't hold your breath. Think about it... For a decompiler to work
properly, either 1) every compiler would have to generate substantially
identical code, even with full optimization turned on, or 2) it would have to
recognize the indivdual output of every compiler's code generator.

  If the first case were to be correct, there would be no more need for
compiler benchmarks since every one would work the same. For the second case
to be true would require in immensely complex program that had to change with
every new compiler release.

  OK, so what about specific decompilers for specific compilers - say a
decompiler designed to only work on code generated by, say, BC++ 3.1? This
gets us right back to the optimization issue. Code written for clarity and
understandability is often inefficient. Code written for maximum performance
(speed or size) is often cryptic (at best!) Add to this the fact that all
modern compilers have a multitude of optimization switches to control which
optimization techniques to enable and which to avoid. The bottom line is
that, for a reasonably large, complex source module, you can get the compiler
to produce a number of different object modules simply by changing your
optimization switches, so your decompiler will also have to be a deoptimizer
which can automagically recognize which optimization strategies were enabled
at compile time.

  OK, let's simplify further and specify that you only want to support one
specific compiler and you want to decompile to the most logical source code
without trying to interpret the optimization. What then? A good optimizer can
and will substantially rewrite the internals of your code, so what you get
out of your decompiler will be, not only cryptic, but in many cases, riddled
with goto statements and other no-no's of good coding practice. At this
point, you have decompiled source, but what good is it?

  Like I said, don't hold your breath. As technology improves to where
decompilers may become more feasible, optimizers and languages (C++, for
example, would be a significantly tougher language to decompile than C) also
conspire to make them less likely.

  For years Unix applications have been distributed in shrouded source form
(machine but not human readable -- all comments and whitespace removed,
variables names all in the form OOIIOIOI, etc.), which has been a quite
adequate means of protecting the author's rights. It's very unlikely that
decompiler output would even be as readable as shrouded source.