GHCi and C++.

Wolfgang Thaller wolfgang.thaller at
Fri Feb 25 13:58:52 EST 2005

> During my ongoing research on "doing whatever I feel like", I
> discovered that using C++ libaries in GHCi (no problems with GHC)
> wasn't as pleasant as I had hoped.
> Apparently C++ sources requires to be linked with crtbegin.o and
> crtend.o (and others?) and I was wondering how to solve this nicely.
> Any hints or pointers would be greatly appreciated.

I think the files crtbegin.o and crtend.o are Linux-specific or maybe 
GNU-binutils-specific. Different platforms tend to have different 
strange requirements for C++ code.

Loading shared libraries that happen to be written in C++ into GHCi 
shouldn't be a problem (or is it? definitely works on Mac OS X). 
Loading C++ .o files is a different story.

Generally speaking, there are at least two things that set C++ .o files 
apart from "normal" C .o files:

*) static constructors/destructors

Sometimes there are pieces of code that expect to be called before 
main() or at program termination. The GHCi Linker doesn't support this, 
so some code may crash because things haven't been initialised 

*) multiple definitions

There is often some code in C++ header files (e.g. templates, inline 
functions, class members declared in the class declaration). These 
pieces of code are sometimes inlined, but sometimes they are not; in 
that case, gcc generates code for them in every .o file that uses them 
and counts on the linker to just include one version in the final 
executable. The GHCi linker will probably just abort and complain about 
multiply-defined symbols.

The above is just theory, there might be even more problems in practice 
:-( .



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