linking C++ code against library from fortran sources

linking C++ code against library from fortran sources

[Hans Horn]

Hi everybody,

I have a bunch of old numerical fortran77 sources, which I compiled with g77
and archived into, say libMyF77.a.

I want those f77 functions to be called from w/i a c++ program.

Here are my two questions:

1. to satisfy the compiler, I have to declare the functions used as
'extern'. Which language string should I be using?
"FORTRAN" as language string (as I had used on other platforms, such as AIX)
is not recognized by gcc/g++
 gcc/g++ accepts only either "C" or nothing (or ????). Which is the right
one here?
2. the linker complains about the functions used as undefined references. I
think I've told the linker properly, where to look for archives (-L<path to
libMyF77.a> -lMyF77). What am I doing wrong? Do I have to do something
special when archiving? Do I have to raise another magic flag for the
linker????


Any light shed onto the subject is severely appreciated!
Hans


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Re: linking C++ code against library from fortran sources

[Danny Smith]

 --- Hans Horn <hannes@2horns.com> wrote: > Hi everybody,
> 
> I have a bunch of old numerical fortran77 sources, which I compiled with
> g77
> and archived into, say libMyF77.a.
> 
> I want those f77 functions to be called from w/i a c++ program.
> 
> Here are my two questions:
> 
> 1. to satisfy the compiler, I have to declare the functions used as
> 'extern'. Which language string should I be using?
> "FORTRAN" as language string (as I had used on other platforms, such as
> AIX)
> is not recognized by gcc/g++
>  gcc/g++ accepts only either "C" or nothing (or ????). Which is the right
> one here?
> 

As you say, extern "FORTRAN" doesn't work.  It should be extern "C".  Note
that g77 uses C calling convention (__cdecl) by default for Fortran. Other
compilers use PASCAL (__stdcall)

2. the linker complains about the functions used as undefined references.
> I
> think I've told the linker properly, where to look for archives (-L<path
> to
> libMyF77.a> -lMyF77). What am I doing wrong? Do I have to do something
> special when archiving? Do I have to raise another magic flag for the
> linker????
> 

By default, g77 appends an underscore to Fortan names, so you will need to
do same in your C/C++ code.  If you can rebuild the libs, you may add
-fno-underscore option to override this decoration. 

Have a look at either the netlib Lapack++ package (C++ wrappers for Fortran
blas and lapack) or Roldan Pozo's TNT package (a start a templated version
of Lapack++) here: 
http://math.nist.gov/tnt/index.html


Danny
 

> Any light shed onto the subject is severely appreciated!
> Hans
> 
> 
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