Passing Fortran files through the C preprocessor

A common programming practice is to pass files through the C preprocessor (cpp). cpp can include or omit lines from the output file based on user-specified conditions ("conditional compilation"). It can also perform string substitution ("macro expansion").

XL Fortran can use cpp to preprocess a file before compiling it.

To call cpp for a particular file, use a file suffix of .F, .F77, .F90, .F95, .F03, or .F08. Each .F* file filename.F* is preprocessed into an intermediate file. You can save the intermediate file by specifying the -d compiler option; otherwise, the file is deleted. If you specify the -d option, the intermediate file name is Ffilename.f*. Otherwise, the intermediate file name is /tmpdir/F8xxxxxx, where x is an alphanumeric character and tmpdir is the contents of the TMPDIR environment variable or, if you have not specified a value for TMPDIR, /tmp. If you only want to preprocess and do not want to produce object or executable files, specify the -qnoobject option also.

When XL Fortran uses cpp for a file, the preprocessor will emit #line directives unless you also specify the -d option. The #line directive associates code that is created by cpp or any other Fortran source code generator with input code that you create. The preprocessor may cause lines of code to be inserted or deleted. Therefore, the #line directives that it emits can be useful in error reporting and debugging, because they identify the source statements found in the preprocessed code by listing the line numbers that were used in the original source.

The _OPENMP C preprocessor macro can be used to conditionally include code. This macro is defined when the C preprocessor is invoked and when you specify the -qsmp=omp compiler option. An example of using this macro follows:

      program par_mat_mul
        implicit none
        integer(kind=8)                 ::i,j,nthreads
        integer(kind=8),parameter       ::N=60
        integer(kind=8),dimension(N,N)  ::Ai,Bi,Ci
        integer(kind=8)                 ::Sumi
#ifdef _OPENMP
	        integer omp_get_num_threads
#endif

	        common/data/ Ai,Bi,Ci
!$OMP   threadprivate (/data/)

!$omp   parallel
	        forall(i=1:N,j=1:N) Ai(i,j) = (i-N/2)**2+(j+N/2)
	        forall(i=1:N,j=1:N) Bi(i,j) = 3-((i/2)+(j-N/2)**2)
!$omp   master
#ifdef _OPENMP
	        nthreads=omp_get_num_threads()
#else
        nthreads=8
#endif
!$omp   end master
!$omp   end parallel

!$OMP parallel default(private),copyin(Ai,Bi),shared(nthreads)
!$omp do
      do i=1,nthreads
	        call imat_mul(Sumi)
      enddo
!$omp end do
!$omp end parallel

	    end

See Conditional compilation in the Language Elements section 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.

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