随着C数组，为什么是这样一个[5] == 5 [A]？ [英] With C arrays, why is it the case that a[5] == 5[a]?

问题描述

由于乔尔在堆栈溢出播客＃34 中的 C语言程序设计（又名：K＆安培; R），有在C数组的这个属性的记载： A [5] == 5 [A]

As Joel points out in Stack Overflow podcast #34, in C Programming Language (aka: K & R), there is mention of this property of arrays in C: a[5] == 5[a]

乔尔说，这是因为指针算法，但我还是不明白。 为什么 A [5] == 5 [A]

Joel says that it's because of pointer arithmetic but I still don't understand. Why does a[5] == 5[a]?

推荐答案

C标准定义了 [] 运算符如下：

The C standard defines the [] operator as follows:

A [B] == *（A + B）

所以 A [5] 将计算为：

*(a + 5)

和 5 [A] 将计算为：

*(5 + a)

A 是一个指向数组的第一个元素。 A [5] 是这5 元素进一步从 A 的价值，这是同 *（A + 5），并从我们知道这些都是平等的小学数学。 （加法是可交换。）

a is a pointer to the first element of the array. a[5] is the value that's 5 elements further from a, which is the same as *(a + 5), and from elementary school math we know those are equal. (Addition is commutative.)

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