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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