When code is being generated by a C compiler to be called by Fortran
programs, as in the netCDF F77 interface, we have to worry about the
Fortran compiler's name mangling. The G95 documentation describes its
default behaviour thus: "G95 follows the f2c convention of adding an
underscore to public names, or two underscores if the name contains an
underscore." The other commonly used compiler that follows this
convention is G77 (but its Gnu successor Gfortran just uses a single
underscore).
The f2c one/two-underscore behaviour is rather difficult to handle, as I
found out when trying to build the MITgcm ocean model, see here:
http://forge.csail.mit.edu/pipermail/mitgcm-support/2006-October/004374.html
So I have decided to become 100% second-underscore-free. To do this I
had to rebuild netCDF. Here is the necessary configure statement (used
successfully with 3.6.2-beta4 on Linux, Cygwin and MSYS+MinGW):
CC=gcc FC=g95 CPPFLAGS=-DpgiFortran FFLAGS=-fno-second-underscore
FCFLAGS=-fno-second-underscore ./configure
If you get it wrong, "make" completes OK, but "make test" fails when
testing the Fortran code.
Why am I sharing this with the group? Partly for posterity (AKA Google
searches). But I have three questions/comments:
1. Perhaps this could be made the default? It would break G77
compatibility and cause a bit of confusion in the short term, but in the
long term I think we would all be better off.
2. I have to set both FFLAGS and FCFLAGS? Why? Surely one would do.
3. I note that the configure script reports (for example): "checking for
C-equivalent to Fortran routine SUB... sub_". I haven't looked at the
configure code, but I assume it is trying different C names (sub, sub_,
SUB, etc) until it gets the right one. The subroutine/function names in
the netCDF-3 F77 interface all have underscores. So why not do the test
with a name that includes an underscore? Then the f2c name-mangling
could be handled automagically?
--
Mark Hadfield "Kei puwaha te tai nei, Hoea tahi tatou"
m.hadfield@xxxxxxxxxx
National Institute for Water and Atmospheric Research (NIWA)
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