HP Fortran Programmer's Guide (B3908-90031; September 2011)

Migrating to HP Fortran
Incompatibilities with HP FORTRAN 77
Chapter 10 223
DOUBLE PRECISION x = 3.1415926535
will initialize x to only 32 bits worth of the constant because it interprets the constant as single precision.
Under HP Fortran, a constant must have a D exponent or a KIND suffix to be interpreted as double precision.
In programs that use double precision exclusively, you should consider using the
+real_constant=double option, which causes real constants to default to double precision. For more
information, refer to “Controlling data storage” on page 99.
Intrinsic functions
The Fortran 90 standard has introduced new intrinsics that may collide with function or subroutine names in
FORTRAN 77 code. You can resolve such collisions by declaring all procedures that you have written—but
especially those that have the same name as nonstandard HP Fortran intrinsics—with the EXTERNAL
statement. For a list of nonstandard HP Fortran intrinsics, see Table 11-4 on page 239.
Also, HP FORTRAN 77 allows intrinsics to accept a wider variety of argument types than HP Fortran does.
For example, in HP FORTRAN 77 the MAX and MIN intrinsics can take arguments of different types, while
HP Fortran follows the standard and requires all arguments to be of the same type. The HP Fortran version
of the TIME intrinsic takes a CHARACTER* argument; it will not accept an integer. Other intrinsics are
similarly affected.
For a full description of all HP Fortran intrinsics, refer to the HP Fortran Programmer's Reference.
Procedure calls and definitions
When defining a procedure or making a procedure call, HP Fortran makes the following requirements,
which HP FORTRAN 77 overlooks:
• Function references must include the parentheses for the argument list, even when no arguments are
supplied. For example, if foo is a user-defined function returning CHARACTER*10, HP FORTRAN 77
permits LEN(foo) and returns 10. HP Fortran requires LEN(foo()).
• The argument list must not contain any extraneous commas, which HP FORTRAN 77 allows as
“placeholders” for missing arguments. For example, the following is acceptable to f77 but not f90:
call foo (a,)
To specify optional arguments in HP Fortran, use the OPTIONAL statement.
• The SYSTEM INTRINSIC directive, by which HP FORTRAN 77 determines interfaces, is not
supported by HP Fortran.
• In HP Fortran, recursive procedures must be so declared with the RECURSIVE keyword;
HP FORTRAN 77 allows recursive procedures by default.