Q48056: L2029: "Unresolved Externals"; FORTRAN Variable Name Limit

Article: Q48056
Product(s): See article
Version(s): 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | SR# S890811-30 B_BasicCom H_Fortran | mspl13_basic
Last Modified: 21-DEC-1989

When LINKing inter-language object modules between QuickBASIC and
FORTRAN, the error message L2029 "Unresolved Externals" may be
displayed because of lengthy variable names. QuickBASIC allows
variable names to extend to 40 characters, all of which are
significant; however, depending on the version of FORTRAN, either 6 or
31 characters are significant.

This information applies to Microsoft QuickBASIC Versions 4.00, 4.00b,
4.50, to Microsoft BASIC Compiler Versions 6.00 and 6.00b for MS-DOS,
and to Microsoft BASIC PDS Version 7.00 for MS-DOS.

When linking QuickBASIC and FORTRAN object files, be careful of which
version of FORTRAN is being used and with what directives. When long
SUBroutine or FUNCTION names are used, FORTRAN may truncate the name
depending on the version and therefore cause the linker error message
L2029 "Unresolved Externals."

Microsoft FORTRAN Version 4.10 allows for variable names to be up to
31 characters, all of which are considered significant. However, the
default option for Version 4.10 is to truncate at the standard six (6)
characters. This can cause problems when BASIC is calling a SUB or
FUNCTION name that is greater than six characters in length.

Microsoft FORTRAN Version 5.00 also allows variable names to be up to
31 characters, all of which are considered significant. This is the
default option, unlike FORTRAN Version 4.10. No variables are
truncated unless they extend beyond the 31-character limit.

FORTRAN offers the following three methods for alleviating this
variable truncation and allows the programmer to easily change the way
the FORTRAN compiler interprets the variable names.

1. The compiler directive /4{Y|N}t allows you to change the
   translation method on the command line. /4Yt causes the FORTRAN 77
   defaults to be in effect. Variable names are truncated at 6
   characters in length. This is the default for FORTRAN Version 4.10.
   /4Nt allows the compiler to use Microsoft's 31 significant character
   variable names. This is the default for FORTRAN Version 5.00.

2. The metacommand $STRICT can be placed directly into the FORTRAN
   code to allow different interpretations of the variable names. When
   the $STRICT metacommand is applied, FORTRAN 77 standards will be
   assumed. For FORTRAN Version 4.10 this is the default, but for
   FORTRAN Version 5.00, $NOSTRICT is the default.

3. The metacommand $TRUNCATE can be placed directly in the FORTRAN
   code to force whether variable names are truncated at the 6
   character limit or $NOTRUNCATE can be used to force 31 character
   variable names. $TRUNCATE is the default for FORTRAN Version 4.10,
   and $NOTRUNCATE is the default for FORTRAN Version 5.00.

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 1986-2002.