Same type defined in two header files

Question

In the source code of MINIX 3 described in Tanenbaum's MINIX book, the line typedef void _PROTOTYPE( (*sighandler_t),(int) ); appears in both include/signal.h and sys/types.h. Why is it defined twice?

EDIT: In sys/types.h some of the surrounding code is:

#ifndef _TYPES_H
#define _TYPES_H

#ifndef _ANSI_H
#include <ansi.h>
#endif

/* ........(too long to write)....... */

#if _EM_WSIZE == 2
/*typedef unsigned int Ino_t; Ino_t is now 32 bits */
typedef unsigned int Zone1_t;
typedef unsigned int Bitchunk_t;
typedef unsigned int Bitchunk_t;
typedef unsigned int U16_t;
typedef unsigned int _mnx_Mode_t;

#else /* _EM_WSIZE == 4, or _EM_WSIZE undefined */
/* typedef int Ino_t; Ino_t is now 32 bits */
typedef int Zone1_t;
typedef int Bitchunk_t;
typedef int U16_t;
typedef int _mnx_Mode_t;

#endif /* _EM_WSIZE == 2, etc */

/* Signal handler type, e.g. SIG_IGN */
typedef void _PROTOTYPE( (*sighandler_t), (int) );

And in include/signal.h:

#ifndef _ANSI_H
#include <ansi.h>
#endif
#ifdef _POSIX_SOURCE
#ifndef _TYPES_H
#include <sys/types.h>
#endif
#endif

/* .......(too long to write)....... */

/* POSIX requires the following signals to be defined, even if they are
 * not supported. Here are the definitions, but they are not supported.
*/
 #define SIGCONT 18 /* continue if stopped */
 #define SIGSTOP 19 /* stop signal */
 #define SIGTSTP 20 /* interactive stop signal */
 #define SIGTTIN 21 /* background process wants to read */
 #define SIGTTOU 22 /* background process wants to write */

/* The sighandler_t type is not allowed unless _POSIX_SOURCE is defined. */
 typedef void _PROTOTYPE( (*__sighandler_t), (int) );

The full files can be found here

You can declare a function prototype as many times as you wish, so long as they are all the same. — Weather Vane, Jul 16 '18 at 20:33
Changed the title to **Same type defined in two different header files** — nanoman, Jul 16 '18 at 20:34
@WeatherVane what would some valid reasons be for doing that? — nanoman, Jul 16 '18 at 20:35
Can you show the relevant code snippets? Including surrounding preprocessor directives. I am pretty sure these will be mutually exclusive. — Eugene Sh., Jul 16 '18 at 20:35
There are no typedefs in signal.h for MINIX 3. What source are you looking at? — OregonJim, Jul 16 '18 at 20:40
@OregonJim I am looking at _incude/signal.h_ in **Appendix B** in Tanenbaum's _Operating System Design and Implementation_ book (that is page 649). — nanoman, Jul 16 '18 at 20:45
We don't have this book. So, please find a way to refer us to the code you are talking about. — Eugene Sh., Jul 16 '18 at 20:46
I would check Andy's website for book errata. I have an older Minix 2 edition, and there was a bunch of errata to correct that one. The "live" MINIX 3 code (you can find it on Github, for example) does not have this dual declaration. — OregonJim, Jul 16 '18 at 21:02
Does your compilation encounter both `_PROTOTYPE` definitions? Perhaps they are wrapped with `#if/#ifdef` is such a way only one, at most, is encountered? — chux - Reinstate Monica, Jul 16 '18 at 22:41

0___________ · Answer 1 · 2018-07-16T21:30:18.837

2

if the type is the same you can typedef it as many times as you wish. Having same typedefs in different files of the same project is usually the sign of the bad project design.

typedef int z;
typedef int z;
typedef int z;

typedef z y;
typedef y z;

typedef float (*x[])(int, int);
typedef float (*x[])(int, int);
typedef float (*x[])(int, int);

typedef x m;
typedef m x;

edited Jul 16 '18 at 21:30

answered Jul 16 '18 at 20:52

0___________

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Or the sign of a rapidly evolving project. :) – OregonJim Jul 16 '18 at 21:06

score 1 · Accepted Answer · answered Jul 16 '18 at 23:06

1

Why is it defined twice?

...because humans are fallible. It seems to be nothing but a bug/omission. Minix 3 is an evolving project and that bug eventually got fixed.

answered Jul 16 '18 at 23:06

Kuba hasn't forgotten Monica

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Same type defined in two header files

2 Answers2