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Subject: [Bug libfortran/33079] Optional empty strings do not appear to be 'PRESENT'
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From: "fxcoudert at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>
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------- Comment #1 from fxcoudert at gcc dot gnu dot org  2007-08-15 14:05 -------
The problem is shared by the TRIM and MIN/MAX. It is demonstrated by:

  character(len=1) :: s
  character(len=0) :: s0
  s = " "
  s0 = ""
  call bar ("")
  call bar (s)
  call bar (s0)
  call bar (trim(s))
  call bar (min(s0,s0))
contains
  subroutine bar (s)
    character(len=*), optional :: s
    if (.not. present (S)) call abort
  end subroutine bar
end

The problem is that a zero-length character string isn't NULL, it's "" (ie a
pointer to a '\0'). The following patch fixes it:

Index: intrinsics/string_intrinsics.c
===================================================================
--- intrinsics/string_intrinsics.c      (revision 127490)
+++ intrinsics/string_intrinsics.c      (working copy)
@@ -167,16 +167,21 @@ string_trim (GFC_INTEGER_4 * len, void *
     }
   *len = i + 1;

-  if (*len > 0)
+  if (*len == 0)
+    {
+      /* A zero-length Fortran string is "".  */
+      char * tmp = internal_malloc_size (1);
+      tmp[0] = '\0';
+      *dest = tmp;
+    }
+  else
     {
       /* Allocate space for result string.  */
       *dest = internal_malloc_size (*len);

-      /* copy string if necessary.  */
+      /* Copy string if necessary.  */
       memmove (*dest, src, *len);
     }
-  else
-    *dest = NULL;
 }


@@ -403,14 +408,18 @@ string_minmax (GFC_INTEGER_4 *rlen, void
     }
   va_end (ap);

-  if (*rlen > 0)
+  if (*rlen == 0)
+    {
+      /* A zero-length Fortran string is "".  */
+      char * tmp = internal_malloc_size (1);
+      tmp[0] = '\0';
+      *dest = tmp;
+    }
+  else
     {
       char * tmp = internal_malloc_size (*rlen);
       memcpy (tmp, res, reslen);
       memset (&tmp[reslen], ' ', *rlen - reslen);
       *dest = tmp;
     }
-  else
-    *dest = NULL;
 }
-


-- 

fxcoudert at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |fxcoudert at gcc dot gnu dot
                   |dot org                     |org
             Status|NEW                         |ASSIGNED
           Keywords|                            |patch
   Last reconfirmed|2007-08-15 13:05:53         |2007-08-15 14:05:29
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33079