为char保证是完全的8位长？ [英] Is char guaranteed to be exactly 8-bit long?

问题描述

这就是全部。没有找到任何类似的话题让我忍受的是有的。

That's all. Didn't find any similar topic so bear with me it there is.

推荐答案

ANSI C规范副本，看到的第3.1.2.5 - 类型的：

的对象声明为char类型是
  足够大的存储的任何成员
  基本执行字符集。如果
  所需的源的部件
  字符集列举$ 2.2.1是
  存储在char对象，它的值是
  保证是正的。如果其他
  量被存储在一个字符
  对象，该行为是
  实现定义：值是
  作为符号或者处理
  非负整数。

An object declared as type char is large enough to store any member of the basic execution character set. If a member of the required source character set enumerated in $2.2.1 is stored in a char object, its value is guaranteed to be positive. If other quantities are stored in a char object, the behavior is implementation-defined: the values are treated as either signed or nonnegative integers.

执行字符集的概念被引入的第2.2.1节 - 字符集的

The concept of "execution character set" is introduced in Section 2.2.1 - Character sets.

在换句话说，一个字符必须至少大到足以容纳至少95不同的角色从而弥补了基本执行字符集编码。

In other words, a char has to be at least big enough to contain an encoding of at least the 95 different characters which make up the basic execution character set.

现在加入到该节的 2.2.4.2 - 数值范围的

一个符合标准的实现应
  文件中规定的所有限制
  这一节，并须指明
  在头文件＆LT;＆limits.h中GT; 和
  ＆LT; float.h时方式＆gt;

A conforming implementation shall document all the limits specified in this section, which shall be specified in the headers <limits.h> and <float.h> .

整型尺寸

下面给出的值应
  通过不断的前pressions取代
  适合在#if preprocessing使用
  指令。其
  实现定义值应
  等于或大于在幅度
  （绝对值）的那些中所示，与
  相同的符号。

The values given below shall be replaced by constant expressions suitable for use in #if preprocessing directives. Their implementation-defined values shall be equal or greater in magnitude (absolute value) to those shown, with the same sign.

  为最小位

• 最大数量
    对象不是一个位域
    （字节）结果CHAR_BIT 8

• maximum number of bits for smallest object that is not a bit-field (byte)
  CHAR_BIT 8

类型的对象最小值
  符号字符结果SCHAR_MIN -127

minimum value for an object of type signed char
SCHAR_MIN -127

类型的对象最大值
  符号字符结果SCHAR_MAX +127

maximum value for an object of type signed char
SCHAR_MAX +127

类型的对象最大值
  unsigned char型结果UCHAR_MAX 255

maximum value for an object of type unsigned char
UCHAR_MAX 255

...

所以你有它 - 位在字符数必须至少为8

So there you have it - the number of bits in a char must be at least 8.

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