HP Fortran Programmer's Guide (September 2007)

Calling C routines from HP Fortran

Case sensitivity

Chapter 8184

Before a Fortran program can call this function correctly, it must resolve two issues:

1. The name of the C function contains both uppercase and lowercase letters.

2. The function expects its second argument (the size of the array) to be passed by value.

The following $HP$ ALIAS directive handles both issues:

!$HP$ ALIAS bubblesort = 'BubbleSort'(%REF, %VAL)

The name bubblesort is the alias that Fortran will use to refer to the C function, and the

%REF and %VAL built-in functions change Fortran’s argument-passing conventions to conform

to how the C function expects the arguments to be passed.

The following is an HP Fortran program that uses the $HP$ ALIAS directive to call the C

function correctly.

Example 8-4 test_sort.f90

PROGRAM main

! This program is linked with an object file that contains

! a C function with the following prototype declaration:

! void BubbleSort(int a[], int size);

! The ALIAS directive takes care of the differences

! between C and Fortran regarding case sensitivity

! and argument-passing conventions.

!$HP$ ALIAS bubblesort = 'BubbleSort'(%REF, %VAL)

INTEGER, PARAMETER :: n = 10

INTEGER, DIMENSION(n) :: num=(/5,4,7,8,1,0,9,3,2,6/)

PRINT *, 'Before sorting: ', num

CALL bubblesort(num, n)

PRINT *, 'After sorting: ', num

END PROGRAM main

Here are the command lines to compile, link, and execute the program, followed by the output

from a sample run:

$ cc -Aa -c sort_em.c

$ f90 test_sort.f90 sort_em.o

$ a.out

Before sorting: 5 4 7 8 1 0 9 3 2 6

After sorting: 0 1 2 3 4 5 6 7 8 9