Interlanguage Calls - Call by Value Parameters
In prototype functions with a variable number of arguments-- specified with an
ellipsis, as in function(...)-- the compiler widens all floating-point arguments to
double precision. Integral arguments (except for long int) are widened to
int. Because of this widening, some data types cannot be passed between
Pascal and C without explicit conversions, and Pascal routines cannot have value
parameters of certain data types.
The following information refers to call by value, as in C. In the following list,
arguments are classified as floating values or nonfloating values:
- Each nonfloating scalar argument requires 1 word and appears in that word exactly as it
would appear in a GPR. It is right-justified, if language semantics specify, and is word
- Each float value occupies 1 word, float doubles occupy 2 successive words in the list,
and long doubles occupy either 2 or 4 words, depending on the setting of the the -qldbl128/-qlongdouble option.
- Structure values appear in successive words as they would anywhere in storage,
satisfying all appropriate alignment requirements. Structures are aligned to a fullword
and occupy (sizeof(struct X)+(wordsize-1))/wordsize) fullwords, with any padding at the
end. A structure smaller than a word is left-justified within its word or register. Larger
structures can occupy multiple registers and can be passed partly in storage and partly in
- Other aggregate values are passed val-by-ref; that is, the compiler actually
passes their addresses and arranges for a copy to be made in the invoked program.
- A function pointer is passed as a pointer to the routine's function descriptor. The
first word contains the entry-point address. See Pointers
to Functions for more information.
Interlanguage Calling Conventions
Corresponding Data Types
Use the Subroutine Linkage Conventions in Interlanguage Calls
Sample Program: C Calling Fortran