cpp's most vexing parse

C++ has parsing ambiguity between a function declaration and a constructor invocation when the constructor arguments are temporaries. This is known as the "most vexing parse" problem. C++09 doesn't resolve this ambiguity but there are several things you can do to avert it in the first place. Awareness is the first step.

当参数是临时变量的时候会出现。

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http://www.informit.com/guides/content.aspx?g=cplusplus&seqNum=439