关于在 C 中打包结构是否有任何保证？
举个例子，假设sizeof(double) == 8，是否保证sizeof(struct { double x, y; }) == 16 ？
我知道这个问题背后的意图与严格的别名规则冲突，因此假设禁用了严格的别名，例如对于带有 -fno-strict-aliasing 的 gcc。
为了避免任何进一步的推测:目的是了解结构与其显式打包的对应结构的兼容性。请注意，即使在以下情况下，别名也是相关的:Are C-structs with the same members types guaranteed to have the same layout in memory? .无需担心我想要访问单个字节。
最佳答案
C 标准关于结构打包的唯一规定是 struct 的开头不能存在填充。它不保证字段之间或末尾的填充。
C standard 的第 6.7.2.1 节说了以下关于结构的内容:
15 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.
...
17 There may be unnamed padding at the end of a structure or union.
也就是说，大多数实现往往与结构的打包方式相当一致。大小为 n 字节的非结构变量(或此类变量的数组)往往从 n 字节边界开始。结构中的结构将倾向于根据其子字段的对齐方式进行对齐。
The Lost Art of C Structure Packing对此进行了更详细的介绍。
关于c - 关于 C struct packing 有什么保证吗？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/47662791/