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Static library undefined reference to global or function


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#1 Servant of the Lord   Crossbones+   -  Reputation: 14948

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Posted 26 June 2013 - 11:21 AM

I'm splitting my game into several static libraries for easier use.

I have my Common library, my Engine library, and my Game executable.

 

I've worked hard in the past to remove all globals, but I still have six of them and it'll really be a nuisance to get rid of them.

As an example, one of the globals is a PathResolver that helps resolve magic variables in path names ("%SCRIPTS%/myFolder/myScript.scr") and relative filepaths (making a path relative to something other than the executable). I don't want to pass it in as a parameter to every function that requires it.

 

Since Common.lib and Engine.lib are both static, and Game directly uses both, and Engine directly uses Common, so Engine link to Common or should Game or both?

 

Engine -lCommon

Game -lEngine -lCommon (Common is linked twice - is that the correct way?)

 

I've been encountering some 'undefined reference to...' the global variables. Engine and Common both compile fine, but when Game is compiled, it says 'undefined reference to' the global variable in Common that Engine and Game are both using.

 

It says the error is occurring in the Engine library, "libEngine.a(ApplicationStructure.o):ApplicationStructure.cpp:(.text+0x7d9)"

What's weird is that ApplicationStructure.cpp doesn't even use the global.

 

It also says, "......./mingw32/bin/ld.exe: ...../libEngine.a(ApplicationStructure.o): bad reloc address 0x2c in section `.rdata'"

 

So anyway, I figured that the global variables might be getting stripped out of the libraries. Do I have to export them in some way other than just labelling them as 'extern'? Bear in mind it's a static library - all my other classes and functions I'm not exporting... am I supposed to export them?.

 

Since I thought the globals might be getting stripped out (from trying to research online), I tried to wrap them in functions, and created a function called GetAppDetailsPointer() for one of the globals. Now it says that there is an undefined reference to that function.

 

Any ideas?


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#2 Servant of the Lord   Crossbones+   -  Reputation: 14948

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Posted 26 June 2013 - 06:22 PM

Ah, but ofcourse! I had forgotten that libraries that depend on other libraries must be linked *before* their dependencies are linked. happy.png

I even had a comment two lines above my dependencies to remind me of that. dry.png

 

I'm assuming that I don't need to link Engine to Common, because it already #includes all that it needs to include, and will find the missing variables and functions when Engine and Common are both linked to the executable.


Edited by Servant of the Lord, 26 June 2013 - 06:26 PM.

It's perfectly fine to abbreviate my username to 'Servant' rather than copy+pasting it all the time.

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#3 Cornstalks   Crossbones+   -  Reputation: 6882

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Posted 26 June 2013 - 08:23 PM

I'm assuming that I don't need to link Engine to Common, because it already #includes all that it needs to include, and will find the missing variables and functions when Engine and Common are both linked to the executable.

That's correct, yes (though it has less to do with #includes and more about how the linker resolves symbols). The real fun comes if Common ever needs to link to Engine, and then you have to either link to Engine when you build Common, or specify Engine twice when building Game (once before Common and once after).
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#4 Tribad   Members   -  Reputation: 452

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Posted 27 June 2013 - 01:44 AM

all gnu based linkers should know --start-group --end-group parameters. Libraries that are enclosed within are checked until all dependencies are resolved. This way you do not need to know the order of libraries to put on the command line.

 

If you want to pass these parameters from the gnu compiler to the linker you need -Wl,--start-group and -Wl,--end-group. -Wl tells the compiler to pass it on to the linker.



#5 Cornstalks   Crossbones+   -  Reputation: 6882

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Posted 27 June 2013 - 11:27 AM

*snip*

I always forget about start/end-group. Thanks for reminding me!
[ I was ninja'd 71 times before I stopped counting a long time ago ] [ f.k.a. MikeTacular ] [ My Blog ] [ SWFer: Gaplessly looped MP3s in your Flash games ]

#6 Servant of the Lord   Crossbones+   -  Reputation: 14948

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Posted 27 June 2013 - 11:37 AM

Thanks, Tribad, never knew that trick.


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#7 Khatharr   Crossbones+   -  Reputation: 2616

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Posted 27 June 2013 - 06:58 PM

Nice. That would have helped me out a lot back when I was working with gcc.


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