problems.txt

C语言库函数的源代码,是C语言学习参考的好文档。

+++Date last modified: 05-Jul-1997

=== Portability problems and how to solve some of them ====================

Contents

- Introduction
- Problems with using the ANSI/ISO standard
- Adaptations for specific compilers
  - Turbo C v1.00 (1987)
  - Turbo C v1.50 (1987)
  - Turbo C v2.00
- Some portability notes on specific compilers
  - Turbo C v1.00 (1987)
  - Turbo C v1.50 (1987)
  - Turbo C v2.00

Introduction

When you get sources from someone else, or give sources to someone else,
you would prefer them to compile without problems and to work right.
Regrettably that is not always entirely possible, but there are a great
many things that can be done to make it so. Essentially those many thing
fall into three groups:
- Using the ANSI/ISO standard.
- Using portability #defines for things not addressed by the standard but
  still common among compilers and operating environments, and Public
  Domain sources for less common items. Both of which can often -- if not
  always -- be found in Snippets.
- Using good coding standards. A good example is contained in the file
  C_port.txt. I use most of the items mentioned in C_port.txt. I only
  disagree with one -- the one about using sizeof -- and I have never found
  problems with indenting pre-processor directives to be any problem.


Problems with using the ANSI/ISO standard

Current compilers -- at least for the PC -- have nearly no problems with
the standard. But older compilers sometimes have severe problems with the
standard.
Turbo C v1.5, which I still use often even though I also have a better
compiler, has problems with multiple inclusion of its own .h files and with
missing items. So I created a simple utility, SAFEMINX, to created
'wrappers' for each include file. I could have edited the original .h
files, but this way makes it possible to easily revert to the original
state. Then I:
- renamed TC's include directory to d:\turboc\_include
- created a new directory with the old name
- ran SAFEMINX
- and edited four of the new files.

During testing of a Snippets beta release this reduced the number of
reported errors (compiling all .C files) from over a thousand to only
thirty four! As the four manually edited files -- or rather its contents --
may be of interest to other users of TC1.5 (and probably the even older TC1
too) I include them here. Separated by a line with hyphens.

/*  STDIO.H
    Prevention of double inclusions.
*/

#ifndef SAFE__STDIO_H
#define SAFE__STDIO_H

#include <d:\turboc\_include\STDIO.H>    /* 'original' */

#ifndef FILENAME_MAX
  #define FILENAME_MAX  80
#endif
#ifndef FOPEN_MAX
  #define FOPEN_MAX     OPEN_MAX
#endif

#endif
------------------------
/*  SIGNAL.H
    Prevention of double inclusions.
*/

#ifndef SAFE__SIGNAL_H
#define SAFE__SIGNAL_H

#include <d:\turboc\_include\SIGNAL.H>    /* 'original' */

#define signal ssignal

#endif
------------------------
/*  ASSERT.H
    Prevention of double inclusions.
*/

#ifndef SAFE__ASSERT_H
#define SAFE__ASSERT_H

#include <d:\turboc\_include\ASSERT.H>    /* 'original' */

#include <stdlib.h> /* for abort() */
#include <stdio.h>  /* for fprintf() and stderr */

#endif
------------------------
/*  TIME.H
    Prevention of double inclusions.
*/

#ifndef SAFE__TIME_H
#define SAFE__TIME_H

#include <d:\turboc\_include\TIME.H>    /* 'original' */

typedef long clock_t;
#define clock()         *((clock_t far *)0x0040006cL)
#define CLOCKS_PER_SEC  18.2
#define CLK_TCK         18.2   /* Non-ANSI/ISO but _very_ common. */

#ifndef _SIZE_T         /* from string.h */
#define _SIZE_T
typedef unsigned size_t;
#endif

/* from Snippets strftime.c: */
size_t strftime(char *s, size_t maxs, const char *f, const struct tm *t);

#endif

=== Adaptations for specific compilers ===================================

The following sections contain additions to the indicated files for
specific compilers to make these more compliant with the ANSI/ISO standard.
At the end there are some notes on various compilers which also may be
useful to users of other compilers.

You should compile and run SAFEMINX first!

Please note that this currently may be incomplete for any file. 

--- Turbo C v1.0 (1987) -- Not the C++ version! --------------------------

--- ASSERT.H

#include <stdlib.h> /* for abort() */
#include <stdio.h>  /* for fprintf() amd stderr */


--- FLOAT.H

#define DBL_EPSILON     2.2204460492503131E-16
/* duplicate of (disabled) following section.
   REQUIRED for some Snippets files           
*/

#if 0  /* disables this section because I'm not sure about the values */
       /* This is taken from TC1.5                                    */

#ifndef TC1_FP_ORIGINAL

#undef DBL_MAX_EXP      /* undefine existing values because */
#undef FLT_MAX_EXP      /* they are _very_ probably wrong   */
#undef LDBL_MAX_EXP
#undef DBL_MIN_EXP
#undef FLT_MIN_EXP
#undef LDBL_MIN_EXP

#define DBL_MAX_EXP     +1024
#define FLT_MAX_EXP      +128
#define LDBL_MAX_EXP    +1024

#define DBL_MIN_EXP     -1021
#define FLT_MIN_EXP      -125
#define LDBL_MIN_EXP    -1021

#endif /* TC1_FP_ORIGINAL */

#define DBL_DIG         14
#define FLT_DIG          6
#define LDBL_DIG        14

#define DBL_MANT_DIG    53
#define FLT_MANT_DIG    24
#define LDBL_MANT_DIG   53

#define DBL_EPSILON     2.2204460492503131E-16
#define FLT_EPSILON     1.19209290E-07F
#define LDBL_EPSILON    2.2204460492503131E-16

#define DBL_MIN         2.225073858507201E-16
#define FLT_MIN         1.17549435E-38F
#define LDBL_MIN        2.225073858507201E-16

#define DBL_MAX         1.797693134862316E+308
#define FLT_MAX         3.40282347E+38F
#define LDBL_MAX        1.797693134862316E+308

#define DBL_MAX_10_EXP   +308
#define FLT_MAX_10_EXP    +38
#define LDBL_MAX_10_EXP  +308

#define DBL_MIN_10_EXP   -307
#define FLT_MIN_10_EXP    -37
#define LDBL_MIN_10_EXP  -307

#endif /* if 0 */

--- SIGNAL.H

#define signal ssignal


--- STDIO.H

#define FILENAME_MAX  80
#define FOPEN_MAX     OPEN_MAX

/* duplicated from dos.h: 
   (required to handle the #define for 'remove')
*/
int     _Cdecl unlink(char *filename);

/* added for ANSI compliance:
   WARNING: I only did compilation testing. NO functional testing (yet) !!!
*/
typedef long fpos_t;
#define fgetpos(stream,pos) ((((*(pos))=ftell(stream))==-1) ? -1 : 0 )
#define fsetpos(stream,pos) fseek(stream,*(pos),SEEK_SET)

--- STDLIB.H

#define EXIT_SUCCESS  0
#define EXIT_FAILURE  1

/* duplicated from stddef.h: */
#ifndef NULL
#if defined(__TINY__) || defined(__SMALL__) || defined(__MEDIUM__)
#define NULL    0
#else
#define NULL    0L
#endif
#endif

/* Missing entirely. Value according to doc's: */
#define RAND_MAX  0x7FFF

--- STRING.H

/* duplicated from stddef.h: */
#ifndef NULL
#if defined(__TINY__) || defined(__SMALL__) || defined(__MEDIUM__)
#define NULL    0
#else
#define NULL    0L
#endif
#endif


--- TIME.H

typedef long clock_t;
#define clock()         *((clock_t far *)0x0040006cL)
#define CLOCKS_PER_SEC  18.2
#define CLK_TCK         18.2   /* Non-ANSI/ISO but _very_ common. */

#ifndef _SIZE_T         /* from string.h */
#define _SIZE_T
typedef unsigned size_t;
#endif

/* from Snippets strftime.c: */
size_t strftime(char *s, size_t maxs, const char *f, const struct tm *t);

--- Turbo C v1.5 (1987) --------------------------------------------------

--- ASSERT.H

#include <stdlib.h> /* for abort() */
#include <stdio.h>  /* for fprintf() amd stderr */

--- SIGNAL.H

#define signal ssignal

--- STDIO.H

#define FILENAME_MAX  80
#define FOPEN_MAX     OPEN_MAX

--- TIME.H

typedef long clock_t;
#define clock()         *((clock_t far *)0x0040006cL)
#define CLOCKS_PER_SEC  18.2
#define CLK_TCK         18.2   /* Non-ANSI/ISO but _very_ common. */

#ifndef _SIZE_T         /* from string.h */
#define _SIZE_T
typedef unsigned size_t;
#endif

/* from Snippets strftime.c: */
size_t strftime(char *s, size_t maxs, const char *f, const struct tm *t);


--- Turbo C v2.0 ---------------------------------------------------------

--- STDIO.H

#define FILENAME_MAX  80
#define FOPEN_MAX     OPEN_MAX

--- TIME.H

#define CLOCKS_PER_SEC CLK_TCK

#ifndef _SIZE_T         /* from string.h */
#define _SIZE_T
typedef unsigned size_t;
#endif

/* from Snippets strftime.c: */
size_t strftime(char *s, size_t maxs, const char *f, const struct tm *t);


==== Some portability notes on specific compilers ========================

---- Turbo C v1.00

TC1.0 in not very ANSI/ISO compliant. But most ANSI/ISO items more or less
work correctly. As indicated in the preceding sections there are however
some items missing. In addition to these the following is not there:
- tmpnam() and some associated functions.
- ldiv_t, div_t and associated functions.

In addition strerror() is _NOT_ ANSI/ISO compliant.

TC1.0 does NOT like items with both 'interrupt' and 'far'.
It also does not have the common (Borland) items:
- random() and randomize()
- chsize()
- gotoxy()
- stdprn and stdaux


---- Turbo C v1.50



---- Turbo C v2.00

TC2 considers "#pragma option ..." an error. Enclose these between
"#if defined(__TURBOC__) && __TURBOC__ >0x202" and "#endif".
(For older TC's these #pragma's don't work anyway ...)


--------------------------------------------------------------------------

That's it for the time being. Maybe I'll expand this for the next release
of Snippets. Suggestions and comments are welcome. An overview of what
items the portability files of Snippets deal with could make sense.

=== A.Reitsma, Delft, The Netherlands. 95-10-30 ====== Public Domain =====