[C] Error “initializer element is not constant” and static

嘗試著要在  static 的 struct 成員指向其他 struct 的時候 (也就是巢狀 struct)，必須注意成員必須是 const，而 C 和 C++ 的 const 語意有所出入，需注意之！

It has to do with C language. In C language objects with static storage duration has to be initialized with constant expressions or with aggregate initializers containing constant expressions.

A "large" object is never a constant expression in C, even if the object is declared as const.

Moreover, in C language the term "constant" refers to literal constants (like 1,'a', 0xFF and so on). Const-qualified objects (of any type) are not constants in C language terminology. They cannot be used in initializers of objects with static storage duration, regardless of their type.

For example, this is NOT a constant

const int C = 5; /* not a constant in C */

It would be a constant in C++, but it is not a constant in C. So, if you try doing

static int j = C; /* ERROR */

you will get the same error: an attempt to initialize a static object with a non-constant.

Ref: http://stackoverflow.com/questions/3025050/error-initializer-element-is-not-constant-when-trying-to-initialize-variable-w

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