HP Fortran Programmer's Guide (March 2010)

Porting to HP Fortran
Using porting options
Chapter 11252
Using porting options
HP Fortran provides a number of compile-line options for porting programs. The most
important of these is the +langlvl=90 option. Compiling your program with this option will
cause the compiler to issue warning messages for all nonstandard features.
In addition, HP Fortran includes options that provide compatibility by changing the
compiler’s assumptions about the program or by causing the compiler to generate code that
executes compatibly with the original implementation. The advantage of using options when
porting is that they minimize having to edit and modify source code.
The following sections describe how options can help when porting programs that contain:
• Initialized variables
• Data types that are larger than the default sizes of HP Fortran data types
• Names that clash with HP-specific intrinsics
• Names that end in the underscore character (_)
• One-trip DO loops
• Different formats
• Escape sequences
Uninitialized variables
As noted in “Automatic and static variables” on page 101, the default behavior of
HP Fortran is to allocate storage for program variables from the stack. However, older
implementations of Fortran often allocate static storage for variables. One of the differences
between stack storage and static storage is that static variables are initialized to 0s by the
compiler, whereas automatic variables (variables allocated from the stack) must be explicitly
initialized by the programmer.
Programs written for implementations of Fortran that allocate static storage by default
sometimes rely on the compiler to initialize variables. Compiling and executing such
programs on implementations that allocate stack storage can have disastrous results. To
make HP Fortran compatible with implementations that allocate static storage, compile with
the +save option. This option causes the compiler to act as though all local variables had the
SAVE attribute.