CODEWITHSUNDEEP
c++dll
Nicolas
Nicolas

Reputation: 403

C++ library compiles but does not work like previous version

There is this library which is used as a reference by other programs: https://github.com/RetroAchievements/RASuite/tree/master/RA_Integration

I have downloaded the compiled programs (that come with the compiled library) and they work fine. My goal is to make a change in the library code, re-compile it and replace the DLL of the compiled programs I have downloaded with my own compiled DLL. Like so:

ProgramA.exe
 |_ RA_Integration.dll   < replace with my own (built)

Before even changing the code, I am just trying to compile the DLL and use it along the compiled programs I have downloaded. I am not willing to re-compile the programs themselves because it will be too much work because of dependencies etc. And I also would like to be able to just "ship" the DLL to whoever wants my fix.

So I have downloaded the source code of that library, re-compiled it myself successfully but when I use it instead of the one that comes with the programs, they do not start up (Windows Event Viewer say that there was a problem loading my DLL).

I am assuming that my system have differences with the system that built the original DLL and that it is the reason why it fails. My question is: can I find those differences? Although I am a professional .NET programmer (as in it's my job) I am a C++ newbie and I am having trouble to understand all those linker/precompiler/dependencies/c++ stuff that seem to give different builds/results from a machine to another.

All I have been able to find is that in the project properties the "Platform Toolset" is "Visual Studio 2013 - Windows XP (v120_xp)", therefore I have installed Visual Studio 2013 (with Update 5 since it seems Windows XP support was not present in base VS2013) but that seems to not be enough. I am running Windows 10, which was surely not the OS the original programmer used when they compiled the DLL a couple years ago, but not sure if that matters?

Is there anything that could be found from the DLL itself or from the project that would hint me as to what I need on my system?

Hope that makes sense.

Thanks

Upvotes: 0

Views: 81

Answers (1)

Marcus M&#252;ller
Marcus M&#252;ller

Reputation: 36346

Before even changing the code, I am just trying to compile the DLL and use it along the compiled programs I have downloaded. I am not willing to re-compile the programs themselves because it will be too much work because of dependencies etc. And I also would like to be able to just "ship" the DLL to whoever wants my fix.

Here's your fallacy: your DLL is a linking dependency. You must re-build your application, because obviously, the ABI of the library changed, rendering it incompatible with what your program tries to call in functionality that it expects to be in the DLL.

There's no way around that short of building an ABI-compatible wrapper DLL using your precious programming knowledge :) Finding these differences is hard – because, you could for example export a symbol list from your DLL, which will basically contain all the functions that DLL "offers", but some aspects of how these functions need to be called aren't actually part of that and can only be deducted by a linker (or a skilled person with too much time on their hand and an unhealthy obsession for parsing things in their head) from the C++ source code.

In other words: you changed what you're run-time linking your program against. You must now rebuild your program. End of options!

Upvotes: 1

Related Questions