****ing Fortran

[KrazyHorse]

Why is it that if I do this:

      IMPLICIT DOUBLE PRECISION (A-H, O-Z)
      IMPLICIT INTEGER(I-N)
      ISTART=7
      I = IRCON(ISTART)
      RETURN
      END

      INTEGER FUNCTION IRCON(ISTART)
      IMPLICIT DOUBLE PRECISION (A-H, O-Z)
      IMPLICIT INTEGER(I-N)
      ISTART=5
      RETURN
      END

but if I do this

      IMPLICIT DOUBLE PRECISION (A-H, O-Z)
      IMPLICIT INTEGER(I-N)
      I = IRCON(7)
      RETURN
      END

      INTEGER FUNCTION IRCON(ISTART)
      IMPLICIT DOUBLE PRECISION (A-H, O-Z)
      IMPLICIT INTEGER(I-N)
      ISTART=5
      RETURN
      END

I segfault?

I understand passing by reference, but why can't I simply manipulate ISTART as a local variable when I pass the 7 by value?

[Asher]

own goal

[KrazyHorse]

Reread. I hit alt-s before completing by mistake

[Asher]

I'm assuming IRCON is some function/procedure you wrote.

I'm also assuming it is expecting a memory address, eg a variable name, rather than just a number.

Thus it's trying to access 0x7 in memory, which is outside of its segment, triggering a segfault.

[KrazyHorse]

Can't be that simple because:

      IMPLICIT DOUBLE PRECISION (A-H, O-Z)
      IMPLICIT INTEGER(I-N)
      I = IRCON(7)
      RETURN
      END

      INTEGER FUNCTION IRCON(ISTART)
      IMPLICIT DOUBLE PRECISION (A-H, O-Z)
      IMPLICIT INTEGER(I-N)
      PRINT *, ISTART
      RETURN
      END

outputs 7 to term, not some random string of gibberish

[KrazyHorse]

(by the way, this is obviously not a real program; I hit a segfault and manage to reduce it down to this simple example)

[KrazyHorse]

So fortran understands passing by value because it's got the right integer when I print from the function

But it refuses to manipulate that variable locally. That makes no sense to me.

[KrazyHorse]

(also note that I've fixed the problem by simply using variable names everywhere I call a function, but it still bothers me; this makes no sense)

[Asher]

Which compiler are you using? gcc?

[KrazyHorse]

g77

[KrazyHorse]

g77 has some Fortran90 elements in it (like ENDDO, long variable names etc)

but there shouldn't be major differences in things like call by reference/value, should there (between f77 and g77)

[Asher]

Do you have another compiler or version of the compiler to try? It looks fine to me, but I've not done Fortran in a while now and most of my stuff was not Fortran 77.

[KrazyHorse]

I can try gfortran, I suppose

[Asher]

I sent this to a friend of mine on the IBM Fortran compiler devteam, we'll see what he says.

[KrazyHorse]

gfortran gives same result