如何是BOOL重新$ P $内存psented？ [英] How is a bool represented in memory?

问题描述

由于在文档中已经讨论过 中，一个布尔数据类型占用内存至少为一个字节。类似的问题，有人问这之前（如何一个布尔类型变量存储在内存中？（C ++）），但这种讨论和文档似乎只是讨论一个布尔数据类型占用空间的大小，而不是实际发生的内存的当我这样做：

布尔B =真;

那么，是什么实际上是在内存发生？发生未在存储该信息中使用的7位是什么？是否标准prescribe行为呢？

他们是不确定的？还是因为有人在C ++总部只有做到这一点：

 枚举布尔：CHAR
{
  假= 0，
  真= 1
};
 

解决方案

标准规定布尔值表现为整型，但它没有指定具体的再$在内存不足p $ psentation：

的类型的值布尔或者是真正或假。如下所述，布尔值表现为整型，类型的值布尔参加积分促销的<子>〜C ++ 03 3.9.1§6

的一个整数类型同义词是整型。整型的重新presentations应由使用纯二进制记数系统的定义值的<子>〜C ++ 3.9 03 .1§7

然而，它定义了从布尔的积分提升到 INT ：

类型的右值布尔可转换为类型的右值 INT 与假成为零和真正成为一体。这些转换称为积分促销活动。的 <子>〜C ++ 4.5 03§4-5

，以及从其他类型转换布尔：

零值，空指针值或空成员指针值转换为假;其它任何值转换为真正的 <子>〜C ++ 03 4.12§1

As already discussed in the docs, a bool data type occupies at least a byte of memory. A similar question was asked on SO before (How a bool type variable is stored in memory? (C++)), but this discussion and the documentation only seem to discuss the amount of space occupied by a boolean data type, not what actually happens in memory when I do this:

bool b = true;

So what does actually happen in memory? What happens to the 7 bits that are not used in storing this information? Does the standard prescribe behavior for this?

Are they undefined? Or did someone at C++ headquarters just do this:

enum bool : char 
{
  false = 0,
  true = 1
};

解决方案

Standard states that bool values behave as integral types, yet it doesn't specify their concrete representation in memory:

"Values of type bool are either true or false. As described below, bool values behave as integral types. Values of type bool participate in integral promotions" _{~ C++03 3.9.1 §6}

"A synonym for integral type is integer type. The representations of integral types shall define values by use of a pure binary numeration system" _{~ C++03 3.9.1 §7}

Yet it defines the integral promotion from bool to int:

"An rvalue of type bool can be converted to an rvalue of type int, with false becoming zero and true becoming one. These conversions are called integral promotions." _{~ C++03 4.5 §4-5}

as well as conversion from other types to bool:

"A zero value, null pointer value, or null member pointer value is converted to false; any other value is converted to true." _{~ C++03 4.12 §1}

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