[Haskell-cafe] FFI, C/C++ and undefined references
Brandon S. Allbery KF8NH
allbery at ece.cmu.edu
Wed Jan 13 23:40:45 EST 2010
On Jan 13, 2010, at 23:28 , DNM wrote:
> Sorry. In my haste to paste in the .c file, I left out all the
> statements. I do have #include "srilm.h" there (which to my non-
> C/C++ mind seems stupid -- why the hell would you need to import
> the header file for the code that it's a header *for*?)
Really, the only reason in this case is that there is no equivalent
for `extern "C"' that you can apply to a function definition, only to
a declaration. The rationale is that everything that works with the
function, including its definition, needs to see that declaration, so
rather than repeat it in the definition you #include the declaration.
In GHC, this is the kind of thing that lands in the .hi file; the
tradeoff is you need to have up to date .hi files for everything that
needs to see that information, which can lead to dependency loops.
GHC has a ".hs-boot" hack to work around this. No free lunch....
brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery at kf8nh.com
system administrator [openafs,heimdal,too many hats] allbery at ece.cmu.edu
electrical and computer engineering, carnegie mellon university KF8NH
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