how to modify the code in a exe file after an update - c++

I'm having a complete program, but now, I want it to be able to be updated. So I would like to change the "code" in the executable by the new code without having to recompile it.
Is it possible? If yes, how can I do, I coding in C++ in Qt Creator.
Thanks for any advise/clue

C++ can't do this. With QT, you could have a javascript implementation of the code you want changed and update that.

I did exactly what Jon told me : simply replace the old exe by the new one

While you can't technically do this in C++ without recompiling, if you don't want to rewrite in another programming language, you could write a small helper program that (while the original program is not running) recompiles the first program.
If you really wanted to do this (it's not hard at all) I'd look into GNU g++.
If you're using Windows, you'll probably want MinGW (which I believe comes with g++ installed). Both are free/open source and fall under the GNU GPL (something you need to look at if you are planning on selling your program. However, you're free to give it away)
Basically you could run your program, call another program before closing, and have that program act as a script to call g++ to re-compile your code. I've done this before, but for faster debugging rather than actually releasing a program that works that way.

Not sure this answers your needs, but did you look into the ClickOnce platform? Although the code still gets recompiled on your server the client executable gets updated via ClickOnce.

Related

How do you ascertain that you are running the latest executable?

Every so often I (re)compile some C (or C++) file I am working on -- which by the way succeeds without any warnings -- and then I execute my program only to realize that nothing has changed since my previous compilation. To keep things simple, let's assume that I added an instruction to my source to print out some debugging information onto the screen, so that I have a visual evidence of trouble: indeed, I compile, execute, and unexpectedly nothing is printed onto the screen.
This happened me once when I had a buggy code (I ran out of the bounds of a static array). Of course, if your code has some kind of hidden bug (What are all the common undefined behaviours that a C++ programmer should know about?) the compiled code can be pretty much anything.
This happened me twice when I used some ridiculously slow network hard drive which -- I guess -- simply did not update my executable file after compilation, and I kept running-and-running the old version, despite the updated source. I just speculate here, and feel free to correct me, if such a phenomenon is impossible, but I suspect it has had to do something with certain processes waiting for IO.
Well, such things could of course happen (and they indeed do), when you execute an old version in the wrong directory (that is: you execute something similar, but actually completely unrelated to your source).
It is happening again, and it annoys me enough to ask: how do you make sure that your executable is matching the source you are working on? Should I compare the date strings of the source and the executable in the main function? Should I delete the executable prior compilation? I guess people might do something similar by means of version control.
Note: I was warned that this might be a subjective topic likely doomed to be closed.
Just use ol' good version control possibilities
In easy case you can just add (any) visible version-id in the code and check it (hash, revision-id, timestamp)
If your project have a lot of dependent files and you suspect older version, than "latest", in produced code, you can (except, obvioulsly, good makefile-rules) monitor also version of every file, used for building code (VCS-dependent, but not so heavy trick)
Check the timestamp of your executable. That should give you a hint regarding whether or not it is recent/up-to-date.
Alternatively, calculate a checksum for your executable and display it on startup, then you have a clue that if the csum is the same the executable was not updated.

writing out binary files using xcode

I'm using xcode 6 to code up a C++ file-based array list (vector) for my Data abstractions course. This, of course, requires writing out binary files. I'm using the C-library functions (fopen, fclose,fread,fwrite,fseek, etc.) since I like those more than the C++ functions. I'm having no issues with my code per se. Everything's working fine, but the issue comes when I execute.
Xcode will "run" everything, but it won't give me out a binary file. I think this has something to do with xcode itself not writing out these files since, all in all, it's a pretty costly thing to do. I can do it through the terminal using g++ but it would be a lot easier if I could do it through the xcode compiler so I'm not having to switch to a terminal window every time to test my code. Let me know if you need any clarification and thanks so much in advance.
The issue might be your working directory not being set correctly inside Xcode.
The file is probably getting written, just not to the right place (or the place you expect it).

C++ compilation at runtime

So I watched this video months back where Epic showcased their new Unreal Engine 4 developer features. Sorry I could not find the video but I'll try my best to explain.
The one feature that got my attention was the C++ "on the fly" modification and compilation. The guy showed how he was playing the game in editor and modified some variables in the code, saved it and the changes were immediately mirrored in game.
So I've been wondering... How does one achieve this? Currently I can think of two possible ways: either a hoax and it was only "c style"-scripting language not C++ itself OR it's shared library (read: DLL) magic.
Here's something I whipped up to try myself(simplified):
for(;;)
{
Move DLL from build directory to execution directory
Link to DLL using LoadLibrary() / dlopen() and fetch a pointer to function "foo()" from it
for(;;)
{
Call the function "foo()" found in the dll
Check the source of the dll for changes
If it has changed, attempt to compile
On succesfull compile, break
}
Unload DLL with FreeLibrary() / dlclose()
}
Now that seems to work but I can't help but wonder what other methods are there?
And how would this kind of approach compare versus using a scripting language?
edit: https://www.youtube.com/watch?v=MOvfn1p92_8&t=10m0s
Yes, "hot code modification" it's definitely a capability that many IDEs/debuggers can have to one extent or another. Here's a good article:
http://www.technochakra.com/debugging-modifying-code-at-runtime/
Here's the man page for MSVS "Edit and Continue":
http://msdn.microsoft.com/en-us/library/esaeyddf%28v=vs.80%29.aspx
Epic's Hot Reload works by having the game code compiled and loaded as a dll/.so, and this is then dynamically loaded by the engine. Runtime reloading is then simply re-compiling the library and reloading, with state stored and restored if needed.
There are alternatives. You could take a look at Runtime Compiled C++ (or see RCC++ blog and videos), or perhaps try one of the other alternatives I've listed on the wiki.
As the author of Runtime Compiled C++ I think it has some advantages - it's far faster to recompile since it only compiles the code you need, and the starting point can be a single exe, so you don't need to configure a seperate project for a dll. However it does require some learning and a bit of extra code to get this to work.
Neither C nor C++ require ahead-of-time compilation, although the usual target environments (operating systems, embedded systems, high-performance number crunching) often benefit greatly from AOT.
It's completely possible to have a C++ script interpreter. As long as it adheres to the behavior in the Standard, it IS C++, and not a "hoax" as you suggest.
Replacement of a shared library is also possible, although to make it work well you'll need a mechanism for serializing all state and reloading it under the new version.

C++ Video Game Programming IDE

I am looking for a C++ IDE in which I can actively play the game and test the updates live instead of testing it, redoing th code, compiling it and running it again. I'm running Windows 7 x86 professional.
This isn't really an answer, and so probably shouldn't get upvotes, but has information.
I don't know of any C++ IDE that can do runtime updates of code, but it's definitely not impossible. There's lots of C++ assemblers which already JIT code, live updates is merely the next step that no IDE has taken quite yet that I know of.
asmjit can JIT C++
Visual Studio can JIT C++/CLI (which isn't quite C++) (RMartinho corrects that VIsual Studio compiles C++/CLI to IL, and then JITs the IL. Tehcnically different.)
cling uses the clang fruntend and LLVM backend, which has a JIT code generation system.
R.Martinho has also reminded me that Microsoft Visual Studio already has this feature. http://msdn.microsoft.com/en-us/library/esaeyddf(v=vs.100).aspx If you "stop" the code, you can make changes, and it will apply those changes and resume execution.
There's an interesting project at http://runtimecompiledcplusplus.blogspot.co.uk/ that is working on this problem and looks like it might work for you; I haven't used it myself but it looks active if still a little raw. It uses the Visual Studio 2010 compiler.
You can't run C++ code without compiling. Minor syntactic differences between languages shouldn't be an issue so you shouldn't limit yourself to just one language.
I suggest you give Unity a chance; there's a fairly robust free version available. You can write scripts in C# (a language similar to C++), or UnityScript (somehting similar to JavaScript) or Boo (similar to Python) and you can test the results right away, without having to compile.
What about Edit and Continue in Visual Studio? In order to use it, you have to pause execution (either by breakpoint or Pause button), recompile and resume. Note, that you can edit the code while the program is running. I know you can't test the game live, but you don't have to reload resources etc. It's IDE integration makes it really easy and straightforward to use.
If you want changes to be visible live, though, consider using script language such as Lua. One of their purposes is what you want to achieve.
I've listed the options for runtime compilation of C++ code on the alternatives wiki page of Runtime Compiled C++.
From the sounds you may interested in either Recode or Alcanterea.
Organize your C++ game to use plugins, and add a feature to load a new (binary version of) plugin during the game.
Then, you could play your game, recompile a plugin, reload it (so invoke your dynamic linker at runtime), and continue playing.
It is not failproof, but it might usually work.
Of course you cannot unload a plugin which has some active call frame on the (or some thread's) call stack. I would suggest to avoid unloading old plugins...

Is there a decompiler that will work on Visual Studio 6 C++

I have a project that I am trying to fix from a guy that left (let go) from my company. He has violated every fundamental principle of software engineering, not using source control, not backing up the source before you make more changes, etc. etc.
I need to make changes to an application that is in the field and I don't have the original source code, but I have an executable. What I need is a decompiler that will decompile a Visual Studio 6 C++ application and provide me with some type of source code. Anyone got any ideas.....
Well there's the Decompiler from Hex-Rays: https://www.hex-rays.com/products/decompiler/
It is pretty good for the fact that it is creating C code from Assembler but it works pretty good. It's also pretty expensive
Edit: Additional note it is combined with IDA Pro the pretty well-known disassembler from them. That already can show you a lot of information in the combination with the decompiler it is even easier to reverse code.
I've used RecStudio (rec22) and IDAPro to try and decompile a C++ project, together they probably wouldn't have been enough to do the job I had except that I worked out the demo project the program was based on so they gave just enough info that I could make something like the same project again.
In the end one other thing I was doing was compiling code that I thought matched and checking that I got the same result in the decompiler.
Good Luck.
Decompile to what - assembler?
There isn't anything that is going to give you meaningfull C from an exe.