ios_base

想问一下ios_base和ios关系，使用ios::out 和ios_base::out 貌似效果一样

C/C++ code

Bitmask type to represent stream error state flags.

See also
ios::rdstate     Get error state flags (public member function)
ios::setstate     Set error state flag (public member function)
ios::good     Check if the state of the stream is good for i/o operations. (public member function)
ios::bad     Check if badbit is set (public member function)
ios::fail     Check if either failbit or badbit is set (public member function )
ios::eof     Check if eofbit is set (public member function)

出处：http://www.cplusplus.com/reference/iostream/ios_base/iostate/

以上可见，ios_base主要是定义存储流状态的标志枚举类型，和ios是继承关系。