intptr_t、uintptr_t数据类型的解析

https://blog.csdn.net/cs_zhanyb/article/details/16973379

2013年11月26日 22:20:09 binggo 阅读数：14066

最近开始研读Nginx的源代码，首先就遇到如下的代码：

typedef intptr_t ngx_int_t;
typedef uintptr_t ngx_uint_t;

intptr_t和uintptr_t是什么类型？以前没见过，于是查了一下。

这两个数据类型是ISO C99定义的，具体代码在linux平台的/usr/include/stdint.h头文件中。

该头文件中定义intptr_t和uintptr_t这两个数据类型的代码片段如下：

/* Types for `void *' pointers. */
#if __WORDSIZE == 64
# ifndef __intptr_t_defined
typedef long int intptr_t;
# define __intptr_t_defined
# endif
typedef unsigned long int uintptr_t;
#else
# ifndef __intptr_t_defined
typedef int intptr_t;
# define __intptr_t_defined
# endif
typedef unsigned int uintptr_t;
#endif

在64位的机器上，intptr_t和uintptr_t分别是long int、unsigned long int的别名；在32位的机器上，intptr_t和uintptr_t分别是int、unsigned int的别名。

那么为什么要用typedef定义新的别名呢？我想主要是为了提高程序的可移植性（在32位和64位的机器上）。很明显，上述代码会根据宿主机器的位数为intptr_t和uintptr_t适配相应的数据类型。

另外，如注释所言，定义这两个数据类型别名也是为了“void *”指针。

在C语言中，任何类型的指针都可以转换为void *类型，并且在将它转换回原来的类型时不会丢失信息。

[root@d ~]# cat /proc/version

Linux version 3.10.0-123.9.3.el7.x86_64 (builder@kbuilder.dev.centos.org) (gcc version 4.8.2 20140120 (Red Hat 4.8.2-16) (GCC) ) #1 SMP Thu Nov 6 15:06:03 UTC 2014

[root@d ~]# cat /usr/include/stdint.h

/* Copyright (C) 1997,1998,1999,2000,2001,2006 Free Software Foundation, Inc.

   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or

   modify it under the terms of the GNU Lesser General Public

   License as published by the Free Software Foundation; either

   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,

   but WITHOUT ANY WARRANTY; without even the implied warranty of

   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public

   License along with the GNU C Library; if not, see

   <http://www.gnu.org/licenses/>.  */

/*

 *      ISO C99: 7.18 Integer types <stdint.h>

 */

#ifndef _STDINT_H

#define _STDINT_H       1

#include <features.h>

#include <bits/wchar.h>

#include <bits/wordsize.h>

/* Exact integral types.  */

/* Signed.  */

/* There is some amount of overlap with <sys/types.h> as known by inet code */

#ifndef __int8_t_defined

# define __int8_t_defined

typedef signed char             int8_t;

typedef short int               int16_t;

typedef int                     int32_t;

# if __WORDSIZE == 64

typedef long int                int64_t;

# else

__extension__

typedef long long int           int64_t;

# endif

#endif

/* Unsigned.  */

typedef unsigned char           uint8_t;

typedef unsigned short int      uint16_t;

#ifndef __uint32_t_defined

typedef unsigned int            uint32_t;

# define __uint32_t_defined

#endif

#if __WORDSIZE == 64

typedef unsigned long int       uint64_t;

#else

__extension__

typedef unsigned long long int  uint64_t;

#endif

/* Small types.  */

/* Signed.  */

typedef signed char             int_least8_t;

typedef short int               int_least16_t;

typedef int                     int_least32_t;

#if __WORDSIZE == 64

typedef long int                int_least64_t;

#else

__extension__

typedef long long int           int_least64_t;

#endif

/* Unsigned.  */

typedef unsigned char           uint_least8_t;

typedef unsigned short int      uint_least16_t;

typedef unsigned int            uint_least32_t;

#if __WORDSIZE == 64

typedef unsigned long int       uint_least64_t;

#else

__extension__

typedef unsigned long long int  uint_least64_t;

#endif

/* Fast types.  */

/* Signed.  */

typedef signed char             int_fast8_t;

#if __WORDSIZE == 64

typedef long int                int_fast16_t;

typedef long int                int_fast32_t;

typedef long int                int_fast64_t;

#else

typedef int                     int_fast16_t;

typedef int                     int_fast32_t;

__extension__

typedef long long int           int_fast64_t;

#endif

/* Unsigned.  */

typedef unsigned char           uint_fast8_t;

#if __WORDSIZE == 64

typedef unsigned long int       uint_fast16_t;

typedef unsigned long int       uint_fast32_t;

typedef unsigned long int       uint_fast64_t;

#else

typedef unsigned int            uint_fast16_t;

typedef unsigned int            uint_fast32_t;

__extension__

typedef unsigned long long int  uint_fast64_t;

#endif

/* Types for `void *' pointers.  */

#if __WORDSIZE == 64

# ifndef __intptr_t_defined

typedef long int                intptr_t;

#  define __intptr_t_defined

# endif

typedef unsigned long int       uintptr_t;

#else

# ifndef __intptr_t_defined

typedef int                     intptr_t;

#  define __intptr_t_defined

# endif

typedef unsigned int            uintptr_t;

#endif

/* Largest integral types.  */

#if __WORDSIZE == 64

typedef long int                intmax_t;

typedef unsigned long int       uintmax_t;

#else

__extension__

typedef long long int           intmax_t;

__extension__

typedef unsigned long long int  uintmax_t;

#endif

# if __WORDSIZE == 64

#  define __INT64_C(c)  c ## L

#  define __UINT64_C(c) c ## UL

# else

#  define __INT64_C(c)  c ## LL

#  define __UINT64_C(c) c ## ULL

# endif

/* Limits of integral types.  */

/* Minimum of signed integral types.  */

# define INT8_MIN               (-128)

# define INT16_MIN              (-32767-1)

# define INT32_MIN              (-2147483647-1)

# define INT64_MIN              (-__INT64_C(9223372036854775807)-1)

/* Maximum of signed integral types.  */

# define INT8_MAX               (127)

# define INT16_MAX              (32767)

# define INT32_MAX              (2147483647)

# define INT64_MAX              (__INT64_C(9223372036854775807))

/* Maximum of unsigned integral types.  */

# define UINT8_MAX              (255)

# define UINT16_MAX             (65535)

# define UINT32_MAX             (4294967295U)

# define UINT64_MAX             (__UINT64_C(18446744073709551615))

/* Minimum of signed integral types having a minimum size.  */

# define INT_LEAST8_MIN         (-128)

# define INT_LEAST16_MIN        (-32767-1)

# define INT_LEAST32_MIN        (-2147483647-1)

# define INT_LEAST64_MIN        (-__INT64_C(9223372036854775807)-1)

/* Maximum of signed integral types having a minimum size.  */

# define INT_LEAST8_MAX         (127)

# define INT_LEAST16_MAX        (32767)

# define INT_LEAST32_MAX        (2147483647)

# define INT_LEAST64_MAX        (__INT64_C(9223372036854775807))

/* Maximum of unsigned integral types having a minimum size.  */

# define UINT_LEAST8_MAX        (255)

# define UINT_LEAST16_MAX       (65535)

# define UINT_LEAST32_MAX       (4294967295U)

# define UINT_LEAST64_MAX       (__UINT64_C(18446744073709551615))

/* Minimum of fast signed integral types having a minimum size.  */

# define INT_FAST8_MIN          (-128)

# if __WORDSIZE == 64

#  define INT_FAST16_MIN        (-9223372036854775807L-1)

#  define INT_FAST32_MIN        (-9223372036854775807L-1)

# else

#  define INT_FAST16_MIN        (-2147483647-1)

#  define INT_FAST32_MIN        (-2147483647-1)

# endif

# define INT_FAST64_MIN         (-__INT64_C(9223372036854775807)-1)

/* Maximum of fast signed integral types having a minimum size.  */

# define INT_FAST8_MAX          (127)

# if __WORDSIZE == 64

#  define INT_FAST16_MAX        (9223372036854775807L)

#  define INT_FAST32_MAX        (9223372036854775807L)

# else

#  define INT_FAST16_MAX        (2147483647)

#  define INT_FAST32_MAX        (2147483647)

# endif

# define INT_FAST64_MAX         (__INT64_C(9223372036854775807))

/* Maximum of fast unsigned integral types having a minimum size.  */

# define UINT_FAST8_MAX         (255)

# if __WORDSIZE == 64

#  define UINT_FAST16_MAX       (18446744073709551615UL)

#  define UINT_FAST32_MAX       (18446744073709551615UL)

# else

#  define UINT_FAST16_MAX       (4294967295U)

#  define UINT_FAST32_MAX       (4294967295U)

# endif

# define UINT_FAST64_MAX        (__UINT64_C(18446744073709551615))

/* Values to test for integral types holding `void *' pointer.  */

# if __WORDSIZE == 64

#  define INTPTR_MIN            (-9223372036854775807L-1)

#  define INTPTR_MAX            (9223372036854775807L)

#  define UINTPTR_MAX           (18446744073709551615UL)

# else

#  define INTPTR_MIN            (-2147483647-1)

#  define INTPTR_MAX            (2147483647)

#  define UINTPTR_MAX           (4294967295U)

# endif

/* Minimum for largest signed integral type.  */

# define INTMAX_MIN             (-__INT64_C(9223372036854775807)-1)

/* Maximum for largest signed integral type.  */

# define INTMAX_MAX             (__INT64_C(9223372036854775807))

/* Maximum for largest unsigned integral type.  */

# define UINTMAX_MAX            (__UINT64_C(18446744073709551615))

/* Limits of other integer types.  */

/* Limits of `ptrdiff_t' type.  */

# if __WORDSIZE == 64

#  define PTRDIFF_MIN           (-9223372036854775807L-1)

#  define PTRDIFF_MAX           (9223372036854775807L)

# else

#  define PTRDIFF_MIN           (-2147483647-1)

#  define PTRDIFF_MAX           (2147483647)

# endif

/* Limits of `sig_atomic_t'.  */

# define SIG_ATOMIC_MIN         (-2147483647-1)

# define SIG_ATOMIC_MAX         (2147483647)

/* Limit of `size_t' type.  */

# if __WORDSIZE == 64

#  define SIZE_MAX              (18446744073709551615UL)

# else

#  ifdef __WORDSIZE32_SIZE_ULONG

#   define SIZE_MAX            (4294967295UL)

#  else

#   define SIZE_MAX            (4294967295U)

#  endif

# endif

/* Limits of `wchar_t'.  */

# ifndef WCHAR_MIN

/* These constants might also be defined in <wchar.h>.  */

#  define WCHAR_MIN             __WCHAR_MIN

#  define WCHAR_MAX             __WCHAR_MAX

# endif

/* Limits of `wint_t'.  */

# define WINT_MIN               (0u)

# define WINT_MAX               (4294967295u)

/* Signed.  */

# define INT8_C(c)      c

# define INT16_C(c)     c

# define INT32_C(c)     c

# if __WORDSIZE == 64

#  define INT64_C(c)    c ## L

# else

#  define INT64_C(c)    c ## LL

# endif

/* Unsigned.  */

# define UINT8_C(c)     c

# define UINT16_C(c)    c

# define UINT32_C(c)    c ## U

# if __WORDSIZE == 64

#  define UINT64_C(c)   c ## UL

# else

#  define UINT64_C(c)   c ## ULL

# endif

/* Maximal type.  */

# if __WORDSIZE == 64

#  define INTMAX_C(c)   c ## L

#  define UINTMAX_C(c)  c ## UL

# else

#  define INTMAX_C(c)   c ## LL

#  define UINTMAX_C(c)  c ## ULL

# endif

#endif /* stdint.h */

[root@d ~]#

[root@d ~]# cat /proc/version
Linux version 3.10.0-123.9.3.el7.x86_64 (builder@kbuilder.dev.centos.org) (gcc version 4.8.2 20140120 (Red Hat 4.8.2-16) (GCC) ) #1 SMP Thu Nov 6 15:06:03 UTC 2014
[root@d ~]# cat /usr/include/stdint.h | grep -i UINTPTR
typedef unsigned long int uintptr_t;
typedef unsigned int uintptr_t;
# define UINTPTR_MAX (18446744073709551615UL)
# define UINTPTR_MAX (4294967295U)
[root@d ~]#

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