第一个元素偏移 [英] First element offset

问题描述

这是个保证，结构的第一个元素是0的偏移？
为了更准确，让我们考虑

Is it a WARRANTY, that offset of first element of structure is 0? To be more accurate, lets consider

struct foo {
int a;
double b;
};
struct foo *ptr=malloc(sizeof(struct foo));
int *int_ptr = &ptr->a;
free(int_ptr)

难道garantied，它是有效的始终，任何操作系统或任何其他因素下？

Is it garantied, that it is valid always, under any os or any other factors?

推荐答案

是的，它是保证。将让你一个标准的报价，让我查找。

Yes it is guaranteed. Will get you a standard quote, let me lookup.

C99标准：§6.7.2.1

第12段

在一个结构物中，非比特场部件和单元，其中比特音响视场
  居住有在其声明的顺序增加地址。 一个指向
  结构对象，适宜地转换，指向其初始部件（如该部件是一个
  比特场，然后在它所在的单元），反之亦然。有可能是未命名
  结构对象中填充，而不是在它的开始。

Within a structure object, the non-bit-field members and the units in which bit-fields reside have addresses that increase in the order in which they are declared. A pointer to a structure object, suitably converted, points to its initial member (or if that member is a bit-field, then to the unit in which it resides), and vice versa. There may be unnamed padding within a structure object, but not at its beginning.

这篇关于第一个元素偏移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！