Using this feature is an optimization that reduces overall code size because, by default, even if the code does not throw exceptions, cl still generates stack unwinding information for C++ sources.
使用这个特性可以对减少整体代码的大小进行优化，因为在缺省情况下，即使代码不会引发异常，cl 仍然会为 C++ 源代码生成堆栈展开信息。
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Our c, CL, CLE series of genset adopt half open structure which will reduce noise much.