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70 Pascal 4.0 User’s Guide

You can also separate the compilation and linking or loading steps, as follows:

hostname% pc program_unit.p -c

hostname% pc module_unit.p -c

hostname% pc program_unit.o module_unit.o

In this case, you call pc on each unit with the “compile only” option (-c),

which produces an object ﬁle with the extension .o. When you use this

option, the compiler driver does not call the linker, ld. You then call pc a

second time, giving the names of the object ﬁles, and pc calls pc3 to check for

name and type conﬂicts before calling the linker.

Calling the linker or loader ld(1) directly does not have the same effect as

calling pc; when you call ld(1) directly, the ﬁles are linked and loaded, but

they are not checked for conﬂicts.

Using Units and Header Files

A complex program may have many routines deﬁned in modules. Each

routine must have a declaration (for example, procedure proc; extern;) in

each ﬁle that calls the routine. The easiest way to be sure that you have a

correct and consistent set of declarations is to create a header ﬁle.

A header ﬁle is a ﬁle that contains a set of declarations, nothing else. You use

a header ﬁle by using an include directive to include the header ﬁle in the

compilation.

For example, here is a modiﬁed version of the program, program_unit, that

uses a header ﬁle:

In this case, the content of header.h is very simple:

program program_unit2 (output);

include "header.h"

begin

say_hello

end.

procedure say_hello; extern;

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HP SunSoft Pascal 4.0 Manual de usuario Pagina 94