sizeof的成本是多少? [英] What is the cost of sizeof?

问题描述

sizeof的成本是多少?

What is the cost of sizeof?

我希望:

• sizeof(someclass)可以在编译时知道
• sizeof(someStaticArray)可以在编译时知道
• sizeof(someDynamicArray)在编译时可能未知

那最后一种情况如何工作?

So how does that last case work?

推荐答案

C中的 sizeof 构造是一个完全编译时的构造.没有运行时成本.

The sizeof construct in C is a completely compile time construct. There is no runtime cost.

此规则至少有一个例外:可变长度数组.这些数组的大小是在运行时计算的，并且该大小可被应用于它们的任何 sizeof 运算符重用.

There is at least one exception to this rule: variable length arrays. The size of these arrays are computed at runtime and that size is reused for any sizeof operators applied to them.

请注意，可变长度数组与动态数组之间存在差异.C99中添加了可变长度数组，它们确实支持sizeof运算符

Please note there is a difference between a variable length array and a dynamic one. Variable length arrays were added in C99 and they do support the sizeof operator

• http://en.wikipedia.org/wiki/Sizeof

这篇关于sizeof的成本是多少?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！