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

Debugging
Using debugging lines
Chapter 4 127
Using debugging lines
An HP Fortran program that has been written in fixed source form can contain debugging lines. These are
statements that begin with the letter D or d in column 1. When compiled with the +dlines option, the
debugging lines are treated as statements and compiled; otherwise, they are treated as comments and
ignored. A program that contains debugging lines must also be compiled for fixed source form; that is, the
filename extension must be either .f or .F, or the program must be compiled with the +source=fixed
option.
The +dlines option makes it possible to include WRITE statements as debugging lines in the source file
and to remove them from the production version of the program without having to change source code.
Instead of deleting the WRITE statements when you are ready to build the production version, you recompile
without the +dlines option, or with the +nodlines option.
Although debugging lines are supported by many implementations of Fortran (especially FORTRAN 77), it
is nonstandard and therefore nonportable. Use of this feature is even more restrictive by reason of its being
incompatible with free source form. If you try to compile a Fortran 90 program as free source form and the
program contains debugging lines, the compilation will almost certainly fail with syntax errors.
The C preprocessor (cpp) provides a set of directives that have the same functionality as debugging lines but
are much more powerful and can be used in either fixed or free source form. Although the cpp directives
are not part of standard Fortran 90, they are available on most UNIX systems, such as HP-UX.
The cpp directives are described in the cpp(1) man page. See the HP Fortran Programmer’s Reference for
information about the source form of HP Fortran programs and the +dlines option.