https://blog.csdn.net/cs_zhanyb/article/details/16973379
最近開始研讀Nginx的源代碼，首先就遇到如下的代碼：
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typedef intptr_t ngx_int_t;
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typedef uintptr_t ngx_uint_t;
這兩個數據類型是ISO C99定義的，具體代碼在linux平台的/usr/include/stdint.h頭文件中。
該頭文件中定義intptr_t和uintptr_t這兩個數據類型的代碼片段如下：
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/* Types for `void *' pointers. */
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typedef long int intptr_t;
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typedef unsigned long int uintptr_t;
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typedef int intptr_t;
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typedef unsigned int uintptr_t;
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在64位的機器上，intptr_t和uintptr_t分別是long int、unsigned long int的別名；在32位的機器上，intptr_t和uintptr_t分別是int、unsigned int的別名。
那么為什么要用typedef定義新的別名呢？我想主要是為了提高程序的可移植性（在32位和64位的機器上）。很明顯，上述代碼會根據宿主機器的位數為intptr_t和uintptr_t適配相應的數據類型。
另外，如注釋所言，定義這兩個數據類型別名也是為了“void *”指針。
在C語言中，任何類型的指針都可以轉換為void *類型，並且在將它轉換回原來的類型時不會丟失信息。
[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 ~]#