UINT32_C和uint32_t之间的区别 [英] Difference between UINT32_C and uint32_t

问题描述

据我所知 uint32_t 中的后缀 t 表示 t 类型，但我想知道 C是什么在 UINT32_C 中有什么区别？

解决方案

UINT32_C 是一个宏，它定义类型为 uint_least32_t 的整数常量。例如：

  UINT32_C（123）//可能在uint_least32_t为无符号long 
 //的系统上扩展为123UL //如果uint_least32_t是unsigned int，则仅为123U。 
  

7.20.4.1最小宽度整数常量的宏

1. 宏 INT N _C（ value ） 应扩展为与 int_least N _t 类型相对应的整数常量表达式
   。宏 UINT N _C（ value ）应该将
   扩展为一个与键入 uint_least N _t 。以
   为例，如果 uint_least64_t 是类型 unsigned long long int 的名称，则
   那么 UINT64_C（0x123）可能会扩展为整数常量 0x123ULL 。

因此，在某些罕见的系统上，此常数可能超过32位。

但是，如果您使用的系统中定义了多个8位2的补码类型（大多数现代系统），并且存在 uint32_t ，则这将创建32位常量

它们均在 stdint.h 中定义，自C99以来已成为C标准的一部分。 / p>

As far as I know the suffix t in uint32_t denote type name but I wonder to know what is the C in UINT32_C and what is the differences?

解决方案

UINT32_C is a macro which defines integer constant of type uint_least32_t. For example:

UINT32_C(123) // Might expand to 123UL on system where uint_least32_t is unsigned long
              // or just 123U, if uint_least32_t is unsigned int.

7.20.4.1 Macros for minimum-width integer constants

1. The macro INTN_C(value) shall expand to an integer constant expression corresponding to the type int_leastN_t. The macro UINTN_C(value) shall expand to an integer constant expression corresponding to the type uint_leastN_t. For example, if uint_least64_t is a name for the type unsigned long long int, then UINT64_C(0x123) might expand to the integer constant 0x123ULL.

It is thus possible that this constant is more than 32 bits on some rare systems.

But if you are on a system where multiple of 8-bits 2's complement types are defined (most modern systems), and uint32_t exists, then this creates 32-bit constant.

They all are defined in stdint.h, and have been part of the C standard since C99.

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