在 C11 中向前發表宣告

範圍內的列舉：

...
enum class Status; // Forward declaration 
Status doWork(); // Use the forward declaration
...
enum class Status { Invalid, Success, Fail };
Status doWork() // Full declaration required for implementation
{
    return Status::Success;
}    

無範圍的列舉：

...
enum Status: int; // Forward declaration, explicit type required
Status doWork(); // Use the forward declaration
...
enum Status: int{ Invalid=0, Success, Fail }; // Must match forward declare type
static_assert( Success == 1 );

這裡可以找到一個深入的多檔案示例： Blind fruit merchant 示例