L2029: "Unresolved Externals"; FORTRAN Variable Name Limit (48056)

SUMMARY

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.

MORE INFORMATION

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.

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.
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.
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.