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

Calling C routines from HP Fortran
Case sensitivity
Chapter 8 189
Case sensitivity
Unlike HP Fortran, C is a case-sensitive language. HP Fortran converts all external names to lowercase, and
it disregards the case of internal names. Thus, for example, the names foo and FOO are the same in Fortran.
C, however, is a case-sensitive language: foo and FOO are different in C. If an HP Fortran program is
linked to a C object file and references a C function that uses uppercase characters in its name, the linker will
not be able to resolve the reference.
If case sensitivity is an issue when calling a C function from an HP Fortran program, you have two choices:
• Compile the Fortran program with the +uppercase option, which forces Fortran to use uppercase for
external names.
•Use the $HP$ ALIAS directive to specify the case that Fortran should use when calling an external
name.
It is unusual that all names in the C source file would be uppercase, which would be the only case justifying
the use of the +uppercase option. Therefore, we recommend using the $HP$ ALIAS directive. This
directive enables you to associate an external name with an external name, even if the external name uses
uppercase characters.
The $HP$ ALIAS directive also has the advantage that you can use it with the %REF and %VAL built-in
functions to specify how the arguments are to be passed without having to repeat them at every call site.
Consider the following C source file, which contains a function to sort an array of integers:
Example 8-3 sort_em.c
#include <stdio.h>
void BubbleSort(int a[], int size)
{
int i, j, temp;
for (i = 0; i < size - 1; i++)
for (j = i + 1; j < size; j++)
if (a[i] > a[j])
{
temp = a[i];
a[i] = a[j];
a[j] = temp;
}
}
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.