Calling a C function from within Fortran

[Ashwin_D_]

Hello,
      I am trying to call a C function within a FORTRAN file and I am getting the following error. Same function call works in gcc and gfortran but fails in icc and ifort. Any suggestions ?
Regards,
Ashwin.

[CC] write_geogrid.c:    icc -D_DOUBLEUNDERSCORE -O2 -Wall  -c write_geogrid.c
[FC] geogrid_SRTM.f90:    ifort -D_DOUBLEUNDERSCORE -O2 -Wall -fsecond-underscore -c geogrid_SRTM.f90
ifort: command line warning #10157: ignoring option '-W'; argument is of wrong type
ifort: command line warning #10006: ignoring unknown option '-fsecond-underscore'
[LD] ConvSRTM:        ifort -D_DOUBLEUNDERSCORE -O2 -Wall -fsecond-underscore write_geogrid.o geogrid_SRTM.o -o ConvSRTM
ifort: command line warning #10157: ignoring option '-W'; argument is of wrong type
ifort: command line warning #10006: ignoring unknown option '-fsecond-underscore'
geogrid_SRTM.o: In function `MAIN__':
geogrid_SRTM.f90:(.text+0x983): undefined reference to `write_geogrid_'
make: *** [ConvSRTM] Error 1

This here is my Makefile
CC=icc

# Put your Fortran compiler here
FC=ifort

CPPFLAGS=-D_DOUBLEUNDERSCORE
CFLAGS=-O2 -Wall
FFLAGS=-O2 -Wall -fsecond-underscore

EXEC_SRTM=ConvSRTM
EXEC_LANDUSE=ConvLANDUSE

.SUFFIXES:
.SUFFIXES: .c .f90 .o

all: $(EXEC_SRTM) $(EXEC_LANDUSE)

.c.o:
    @echo -n "[CC] $<:    "
    $(CC) $(CPPFLAGS) $(CFLAGS) -c $<

.f90.o:
    @echo -n "[FC] $<:    "
    $(FC) $(CPPFLAGS) $(FFLAGS) -c $<

$(EXEC_SRTM): write_geogrid.o geogrid_SRTM.o
    @echo -n "[LD] $@:        "
    $(FC) $(CPPFLAGS) $(FFLAGS) write_geogrid.o geogrid_SRTM.o -o $(EXEC_SRTM)
    @echo

$(EXEC_LANDUSE): write_geogrid.o geogrid_LAND.o
    @echo -n "[LD] $@:    "
    $(FC) $(CPPFLAGS) $(FFLAGS) write_geogrid.o geogrid_LAND.o -o $(EXEC_LANDUSE)
    @echo    
clean:
    rm -f *.o $(EXEC_SRTM) $(EXEC_LANDUSE)

[TimP]

second-underscore is a g77 convention, best forgotten with current compilers.   linux default (single appended underscore) is the same for ifort and gfortran.  For portability, you should USE iso_c_binding (for example, gfortran still uses single appended underscore on Windows, while ifort needs additional options for that).

As you saw, ifort rejects -Wall (so don't use it).