在编译时确定结构成员的字节偏移量? [英] Determining struct member byte-offsets at compile-time?

问题描述

我想在编译时找到struct成员的字节偏移量.例如:

I want to find the byte offset of a struct member at compile-time. For example:

struct vertex_t
{
    vec3_t position;
    vec3_t normal;
    vec2_t texcoord;
}

我想知道normal的字节偏移是(在这种情况下，它应该是12.)

I would want to know that the byte offset to normal is (in this case it should be 12.)

我知道我可以使用offsetof，但这是一个运行时函数，我希望不要使用它.

I know that I could use offsetof, but that is a run-time function and I'd prefer not to use it.

我想做到的甚至是可能的吗?

Is what I'm trying to accomplish even possible?

编辑:offsetof在编译时，我很糟糕！

EDIT: offsetof is compile-time, my bad!

推荐答案

offsetof是编译时常量，如果我们查看草稿的C ++标准部分C.3 C标准库段落 2 说:

offsetof is a compile time constant, if we look at the draft C++ standard section C.3 C standard library paragraph 2 says:

C ++标准库提供了来自C库的57个标准宏，如表149所示.

The C++ standard library provides 57 standard macros from the C library, as shown in Table 149.

，并且该表包含offsetof.如果转到C99草案标准部分的7.17 通用定义段落，则 3 包括:

and the table includes offsetof. If we go to the C99 draft standard section 7.17 Common definitions paragraph 3 includes:

offsetof(类型，成员标识符)

offsetof(type, member-designator)

扩展为一个整数常量表达式，其类型为size_t，即 这是以字节为单位的偏移量[...]

which expands to an integer constant expression that has type size_t, the value of which is the offset in bytes [...]

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