如何使用匿名结构/联合编译 C 代码?

I can do this in c++/g++:

struct vec3 { 
    union {
        struct {
            float x, y, z;
        }; 
        float xyz[3];
    }; 
};

那么，

vec3 v;
assert(&v.xyz[0] == &v.x);
assert(&v.xyz[1] == &v.y);
assert(&v.xyz[2] == &v.z);

会起作用.

如何用 gcc 在 c 中做到这一点?我有

typedef struct {
    union {
        struct {
            float x, y, z;
        };
        float xyz[3];
    };
} Vector3;

line 5: warning: declaration does not declare anything
line 7: warning: declaration does not declare anything