c/c++: uint8_t uint16_t uint32_t uint64_t size_t ssize_t数据类型

川长思鸟来 2022-08-10 12:55 327阅读 0赞

原文写的不错，转来收藏，转自： http://wangyisouhuxin.blog.163.com/blog/static/761966592011072348700/?fromdm&fromSearch&isFromSearchEngine=yes

在nesc的代码中，你会看到很多你不认识的数据类型，比如uint8_t等。咋一看，好像是个新的数据类型，不过C语言（nesc是C的扩展）里面好像没有这种数据类型啊！怎么又是u又是_t的？很多人有这样的疑问。论坛上就有人问：以*_t结尾的类型是不是都是long型的？在baidu上查一下，才找到答案，这时才发觉原来自己对C掌握的太少。

那么_t的意思到底表示什么？具体的官方答案没有找到，不过我觉得有个答案比较接近。它就是一个结构的标注，可以理解为type/typedef的缩写，表示它是通过typedef定义的，而不是其它数据类型。

uint8_t，uint16_t，uint32_t等都不是什么新的数据类型，它们只是使用typedef给类型起的别名，新瓶装老酒的把戏。不过，不要小看了typedef，它对于你代码的维护会有很好的作用。比如C中没有bool，于是在一个软件中，一些程序员使用int，一些程序员使用short，会比较混乱，最好就是用一个typedef来定义，如：
typedef char bool;

一般来说，一个C的工程中一定要做一些这方面的工作，因为你会涉及到跨平台，不同的平台会有不同的字长，所以利用预编译和typedef可以让你最有效的维护你的代码。为了用户的方便，C99标准的C语言硬件为我们定义了这些类型，我们放心使用就可以了。

按照posix标准，一般整形对应的*_t类型为：
1字节 uint8_t
2字节 uint16_t
4字节 uint32_t
8字节 uint64_t

附：inttypes.h的内容（不同的服务器会有不同的源文件结构，但原理是一样的，我这里sun服务器inttypes.h引用了int_type.h）

[cpp] view plain copy

  1. bash-3.00$ vi int_types.h
  2. “int_types.h” [Read only] 176 lines, 4367 characters
  3. /*
  4. * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
  5. * Use is subject to license terms.
  6. */
  8. #ifndef _SYS_INT_TYPES_H
  9. #define _SYS_INT_TYPES_H
  11. #pragma ident “@(#)int_types.h 1.10 04/09/28 SMI”
  13. /*
  14. * This file, , is part of the Sun Microsystems implementation
  15. * of defined in the ISO C standard, ISO/IEC 9899:1999
  16. * Programming language - C.
  17. *
  18. * Programs/Modules should not directly include this file. Access to the
  19. * types defined in this file should be through the inclusion of one of the
  20. * following files:
  21. *
  22. * Provides only the “_t” types defined in this
  23. * file which is a subset of the contents of
  24. * . (This can be appropriate for
  25. * all programs/modules except those claiming
  26. * ANSI-C conformance.)
  27. *
  28. * Provides the Kernel and Driver appropriate
  29. * components of .
  30. *
  31. * For use by applications.
  32. *
  33. * See these files for more details.
  34. */
  36. #include
  38. #ifdef __cplusplus
  39. extern “C” {
  40. #endif
  42. /*
  43. * Basic / Extended integer types
  44. *
  45. * The following defines the basic fixed-size integer types.
  46. *
  47. * Implementations are free to typedef them to Standard C integer types or
  48. * extensions that they support. If an implementation does not support one
  49. * of the particular integer data types below, then it should not define the
  50. * typedefs and macros corresponding to that data type. Note that int8_t
  51. * is not defined in -Xs mode on ISAs for which the ABI specifies “char”
  52. * as an unsigned entity because there is no way to define an eight bit
  53. * signed integral.
  54. */
  55. #if defined(_CHAR_IS_SIGNED)
  56. typedef char int8_t;
  57. #else
  58. #if defined(__STDC__)
  59. typedef signed char int8_t;
  60. #endif
  61. #endif
  62. typedef short int16_t;
  63. typedef int int32_t;
  64. #ifdef _LP64
  65. #define _INT64_TYPE
  66. typedef long int64_t;
  67. #else /* _ILP32 */
  68. #if defined(_LONGLONG_TYPE)
  69. #define _INT64_TYPE
  70. typedef long long int64_t;
  71. #endif
  72. #endif
  74. typedef unsigned char uint8_t;
  75. typedef unsigned short uint16_t;
  76. typedef unsigned int uint32_t;
  77. #ifdef _LP64
  78. typedef unsigned long uint64_t;
  79. #else /* _ILP32 */
  80. #if defined(_LONGLONG_TYPE)
  81. typedef unsigned long long uint64_t;
  82. #endif
  83. #endif
  85. /*
  86. * intmax_t and uintmax_t are to be the longest (in number of bits) signed
  87. * and unsigned integer types supported by the implementation.
  88. */
  89. #if defined(_INT64_TYPE)
  90. typedef int64_t intmax_t;
  91. typedef uint64_t uintmax_t;
  92. #else
  93. typedef int32_t intmax_t;
  94. typedef uint32_t uintmax_t;
  95. #endif
  97. /*
  98. * intptr_t and uintptr_t are signed and unsigned integer types large enough
  99. * to hold any data pointer; that is, data pointers can be assigned into or
  100. * from these integer types without losing precision.
  101. */
  102. #if defined(_LP64) || defined(_I32LPx)
  103. typedef long intptr_t;
  104. typedef unsigned long uintptr_t;
  105. #else
  106. typedef int intptr_t;
  107. typedef unsigned int uintptr_t;
  108. #endif
  110. /*
  111. * The following define the fastest integer types that can hold the
  112. * specified number of bits.
  113. */
  114. #if defined(_CHAR_IS_SIGNED)
  115. typedef char int_fast8_t;
  116. #else
  117. #if defined(__STDC__)
  118. typedef signed char int_fast8_t;
  119. #endif
  120. #endif
  121. typedef int int_fast16_t;
  122. typedef int int_fast32_t;
  123. #ifdef _LP64
  124. typedef long int_fast64_t;
  125. #else /* _ILP32 */
  126. #if defined(_LONGLONG_TYPE)
  127. typedef long long int_fast64_t;
  128. #endif
  129. #endif
  131. typedef unsigned char uint_fast8_t;
  132. typedef unsigned int uint_fast16_t;
  133. typedef unsigned int uint_fast32_t;
  134. #ifdef _LP64
  135. typedef unsigned long uint_fast64_t;
  136. #else /* _ILP32 */
  137. #if defined(_LONGLONG_TYPE)
  138. typedef unsigned long long uint_fast64_t;
  139. #endif
  140. #endif
  142. /*
  143. * The following define the smallest integer types that can hold the
  144. * specified number of bits.
  145. */
  146. #if defined(_CHAR_IS_SIGNED)
  147. typedef char int_least8_t;
  148. #else
  149. #if defined(__STDC__)
  150. typedef signed char int_least8_t;
  151. #endif
  152. #endif
  153. typedef short int_least16_t;
  154. typedef int int_least32_t;
  155. #ifdef _LP64
  156. typedef long int_least64_t;
  157. #else /* _ILP32 */
  158. #if defined(_LONGLONG_TYPE)
  159. typedef long long int_least64_t;
  160. #endif
  161. #endif
  163. typedef unsigned char uint_least8_t;
  164. typedef unsigned short uint_least16_t;
  165. typedef unsigned int uint_least32_t;
  166. #ifdef _LP64
  167. typedef unsigned long uint_least64_t;
  168. #else /* _ILP32 */
  169. #if defined(_LONGLONG_TYPE)
  170. typedef unsigned long long uint_least64_t;
  171. #endif
  172. #endif
  174. #ifdef __cplusplus
  175. }
  176. #endif
  178. #endif /* _SYS_INT_TYPES_H */

同理在types.h文件中会有size_t ssize_t的定义，篇幅较长不贴出了。

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