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Using and Porting GNU Fortran

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9.9.7 Ugly Assigned Labels

The `-fugly-assign' option forces g77 to use the same storage for assigned labels as it would for a normal assignment to the same variable.

For example, consider the following code fragment:

 
I = 3
ASSIGN 10 TO I

Normally, for portability and improved diagnostics, g77 reserves distinct storage for a "sibling" of `I', used only for ASSIGN statements to that variable (along with the corresponding assigned-GOTO and assigned-FORMAT-I/O statements that reference the variable).

However, some code (that violates the ANSI FORTRAN 77 standard) attempts to copy assigned labels among variables involved with ASSIGN statements, as in:

 
ASSIGN 10 TO I
ISTATE(5) = I
...
J = ISTATE(ICUR)
GOTO J

Such code doesn't work under g77 unless `-fugly-assign' is specified on the command-line, ensuring that the value of I referenced in the second line is whatever value g77 uses to designate statement label `10', so the value may be copied into the `ISTATE' array, later retrieved into a variable of the appropriate type (`J'), and used as the target of an assigned-GOTO statement.

Note: To avoid subtle program bugs, when `-fugly-assign' is specified, g77 requires the type of variables specified in assigned-label contexts must be the same type returned by %LOC(). On many systems, this type is effectively the same as INTEGER(KIND=1), while, on others, it is effectively the same as INTEGER(KIND=2).

Do not depend on g77 actually writing valid pointers to these variables, however. While g77 currently chooses that implementation, it might be changed in the future.

See section Assigned Statement Labels (ASSIGN and GOTO), for implementation details on assigned-statement labels.


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