XL Fortran Enterprise Edition for AIX : User's Guide - IBM

!$omp end do
!$omp end parallel
end
See Conditional Compilation in the Language Elements section of the XL Fortran
Enterprise Edition for AIX Language Reference for more information on conditional
compilation.
To customize cpp preprocessing, the configuration file accepts the attributes cpp,
cppsuffix, and cppoptions.
The letter F denotes the C preprocessor with the -t and -W options.
Related Information: See “-d Option” on page 106, “-t Option” on page 270, “-W
Option” on page 275, and “Customizing the Configuration
File” on page 15.
cpp Directives for XL Fortran Programs
Macro expansion can have unexpected consequences that are difficult to debug,
such as modifying a FORMAT statement or making a line longer than 72
characters in fixed source form. Therefore, we recommend using cpp primarily for
conditional compilation of Fortran programs. The cpp directives that are most
often used for conditional compilation are #if, #ifdef, #ifndef, #elif, #else, and
#endif.
Passing Options to the C Preprocessor
Because the compiler does not recognize cpp options other than -I directly on the
command line, you must pass them through the -W option. For example, if a
program contains #ifdef directives that test the existence of a symbol named
AIXV4, you can define that symbol to cpp by compiling with a command like:
xlf95 conditional.F -WF,-DAIXV4
Avoiding Preprocessing Problems
Because Fortran and C differ in their treatment of some sequences of characters, be
careful when using /* or */. These might be interpreted as C comment delimiters,
possibly causing problems even if they occur inside Fortran comments. Also be
careful when using three-character sequences that begin with ?? (which might be
interpreted as C trigraphs).
Consider the following example:
program testcase
character a
character*4 word
a = ’?’
word(1:2) = ’??’
print *, word(1:2)
end program testcase
If the preprocessor matches your character combination with the corresponding
trigraph sequence, your output may not be what you expected.
If your code does not require the use of the XL Fortran compiler option
-qnoescape, a possible solution is to replace the character string with an escape
sequence word(1:2) = ’\?\?’. However, if you are using the -qnoescape compiler
option, this solution will not work. In this case, you require a cpp that will ignore
Editing, Compiling, Linking, and Running XL Fortran Programs 41