HP C Programmer's Guide (92434-90009)

50 Chapter3

Calling Other Languages

Comparing HP C and HP Pascal

unsigned int b9 : 1;

} SET_10;

SET_10 s;

Also, the following operation in HP Pascal:

s := s + [9];

has the following corresponding HP C code:

s.b9 = 1;

15.HP C and HP Pascal ﬁle types and I/O operations do not correspond.

Passing Parameters Between HP C and HP Pascal

This section describes additional information on parameter passing.

1. All HP C parameters are passed by value except arrays and functions, which are always

passed as pointers. Reference parameters to HP Pascal can be implemented in two

ways: ﬁrst, by passing the address of an object by applying the address operator & to the

variable; second, by declaring a variable to be a pointer to such a type, assigning an

address to the pointer variable, and passing the pointer.

If an HP Pascal procedure or function has a parameter that is an array by value, it can

be called from HP C by passing a struct that contains an array of the corresponding

type.

2. Be careful when passing strings to HP Pascal. If the routine expects a packed array of

char, be sure to pass a char array. If the routine expects a user-deﬁned string, pass the

structure declared in Note 5 above.

The examples below are HP Pascal and HP C source ﬁles that show the parameter

passing rules. The HP Pascal ﬁle contains 2 subroutines, pass_char_arrays() and

pass_a_string(). The HP C ﬁle contains the main line routine that calls these two

subroutines and displays the results. The HP C program is annotated with the expected

results.

The following is the HP Pascal procedure called from HP C:

$subprogram$

program p;

const len = 10;

type

pac_10 = packed array [1..10] of char;

string_10 = string [len];

function pass_char_arrays (a: pac_10;

var b: pac_10;

c: string_10;

var d: string_10) : integer;

var

i : integer;

ret_val : integer;

begin