为什么.NET可选System.Boolean需要4个字节？ [英] Why in .NET System.Boolean takes 4 byte?

问题描述

为什么可选System.Boolean需要4个字节，即使它只是存储一个状态TRUE或FALSE;其可以存储少于4字节？

Why System.Boolean takes 4 bytes even if it just stores one state TRUE or FALSE; which may be stored less than 4 bytes?

推荐答案

A 布尔实际上只有1个字节，但调整可能会导致在32使用的4个字节比特平台，或者甚至8个字节在64位的平台上。例如，可空＆LT;布尔＆GT; （？又名布尔）的类型采用了全32位或64位，这取决于平台，即使它仅仅由两个布尔取值。 修改：正如乔恩飞碟双向，填充对准不是的总是的present。举个例子，数组可空＆LT;布尔＆GT; S可每个对象，而不是4只2个字节或8

A bool is actually only 1 byte, but alignment may cause 4 bytes to be used on a 32-bit platform, or even 8 bytes on a 64-bit platform. For example, the Nullable<bool> (aka bool?) type uses a full 32 or 64 bits—depending on platform—even though it's comprised of just two bools. EDIT: As pointed out by Jon Skeet, padding for alignment isn't always present. As an example, an array of Nullable<bool>s takes only 2 bytes per object instead of 4 or 8.

不过，即使8位，重新present一个布尔可以被认为是一种浪费，如果你有很多人到店里。出于这个原因，如果你创建具有许多布尔取值为成员（或使用许多类型可空＆LT;＆GT; 类型），和用户类可能会创建它的很多情况下，你可能会考虑使用 BitVector32 代替。该框架本身使用该技术，以减少许多的Windows的内存占用窗体控件，例如。

But even 8 bits to represent a bool can be considered wasteful if you have many of them to store. For this reason, if you create a type that has many bools as members, (or uses many Nullable<> types), and users of your class might create many instances of it, you might consider using a BitVector32 instead. The framework itself uses this technique to reduce the memory footprint of many of the Windows Forms controls, for instance.

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