How to make compile a Fortran program that calls a C function?

[pr0crastin8r]

Hey all,

I am on Windows XP running the Intel Visual Fortran Compiler Version 11.1.065 and the native C compiler in Visual Studio 2008. I am having issues with the magling of symbols between the object files of the two languages that result in unresolved externals in the linker. I was wondering if there are any changes I need to make to my code or command line options I can set on the compiler to make this work. Here is my code:

cshare.f:

[fortran]      program flagtest
         
         logical :: flagSet
         character*32 yes_msg
         character*32 no_msg
         character*32 start_msg
         integer millis

         millis = 1000
         yes_msg = 'Go!'
         no_msg = 'No flag detected, sleeping...'
         start_msg = 'Starting up...'
10       format(a32)


         write(*,10) start_msg

         do while(1==1)
            inquire(FILE="flag", EXIST=flagSet)
            if(flagSet) then
               write(*,10) yes_msg
               call system('DEL flag.txt')
            else
               write(*,10) no_msg
               call csleep(millis)
            endif
         end do
         stop
      end[/fortran]

csleep.c

[cpp]#include 
#include 

int csleep_(int *millis)
{	
   Sleep(*millis);
   printf("What a good night's sleep! A whole %d milliseconds!\n",*millis);
   return(0);
}[/cpp]

Commands:

on Visual Studio command line:
cl -c csleep.c

on ifort command line:
ifort /Qvc9 /c cshare.f
ifort /Qvc9 csleep.obj cshare.obj /exe:csleep

output:
-out:csleep.exe
-subsystem:console
csleep.obj
cshare.obj
cshare.obj : error LNK2019: unresolved external symbol _CSLEEP referenced in function _MAIN__
csleep.exe : fatal error LNK1120: 1 unresolved externals

Can anyone tell me what I need to do differently?

Thanks!

[mecej4]

You may either look up the naming conventions in the Fortran documentation, or let the compiler do it for you in steps.

If you compile the Fortran part stand-alone, you get the message from the linker:

[bash]unresolved external symbol _CSLEEP[/bash]

Therefore, the name of the C function should be "CSLEEP", not "csleep" and no extra underscores are needed. Secondly, subroutines do not return values and cannot have a type. Therefore, the return type of the C function should be void, not int.

With these changes, and compiling with consistent options, I get

[bash]Starting up...
No flag detected, sleeping...
What a good night's sleep! A whole 1000 milliseconds!
No flag detected, sleeping...
What a good night's sleep! A whole 1000 milliseconds!
No flag detected, sleeping...
...[/bash]

[pr0crastin8r]

Thank you! That worked!

[TimP]

There are a perhaps bewildering number of options discussed in the ifort docs. In the case at hand, I don't see a reason for avoiding the portable method, which is the USE ISO_C_BINDING method.