C语言中结构的填充量是否依赖于编译器或定义得当? [英] Is the amount of padding in structure in C is Compiler dependent or well defined?

问题描述

是C struct中的填充量，在标准或编译器和/或目标体系结构相关方面定义良好.我找不到标准的答案.

Is the a amount of padding in C struct well defined in standards or compiler and/or target architecture dependent. I could not find an answer in the standards.

推荐答案

它是实现定义的.根据C99标准的6.7.2.1节:

It is implementation-defined. From section 6.7.2.1 of the C99 standard:

...结构或联合对象的每个非位字段成员在实现定义中对齐 适合其类型的方式...

...Each non-bit-field member of a structure or union object is aligned in an implementation-defined manner appropriate to its type...

...可能未命名 填充在结构对象中，而不是在其开头...

...There may be unnamed padding within a structure object, but not at its beginning...

编译器通常会选择适合底层硬件的排列方式(对齐内容以便于从内存中读取等).

The compiler will typically choose an arrangement that suits the underlying hardware (aligning things to be easy to read from memory, etc.).

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