How to call a C-routine from Fortran

There is usually not major problem to call C-routines from C and vice-versa (as long as the parameters are arrays and scalars). This is the way to use fsecond.

program examp
  double precision :: fsecond, t

  t = fsecond()
!   compute ...
  t = fsecond() - t

  print*, 'time = ', t
 
end program examp

and this is how you compile and link:
 

• Compile fsecond.c once and for all using the C-compiler:
   
  cc -c fsecond.c      this will produce the object file fsecond.o
   
• Compile your Fortranprogram and link with fc (where fc is your compiler, g95, gfortran, ifort, ...)
   
  fc my_prog.f90 fsecond.o