moc_xxxx.cpp 和 xxxx.moc

用qmake处理moc文件:
qmake产生moc_xxxx.cpp并将其编译为可链接的moc_xxxx.o。在某些特定的情况下，可能比较好的用法是先产生moc_xxxx.cpp而不将其编译为*.o文件，然后moc_xxxx.cpp可以通过在xxxx.cpp中添加#include "moc_xxxx.cpp"方式被include。 

stackoverflow上的说明：
http://stackoverflow.com/questions/5854626/qt-signals-and-slots-error-undefined-reference-to-vtable-for

Whenever you declare a QObject inside a filename.cpp file, you should add #include "filename.moc" to the end of your .cpp file and qmake will do the right thing for you. This is the common practice in KDE, for example.

关于moc_xxxx.cpp 和 xxxx.moc的产生：

    when you declare a QObject class in a header file xxxx.h generated file is moc_xxxx.cppwhen you declare a QObject class in a source file xxxx.cpp
generated file is xxxx.moc because if you declare a QObject class in xxxx.h and another in xxxx.cpp the two generated files can not have the same name

它编译是是需要这个文件的，作为库提供给用户使用，不包含它的话用户工程中也会自动生成包含它，这不符封装规则，库的事情库自己应完成。如果库里使用了名字空间，更是这样，用户处理的话(实际上是qmake编译器帮完成的)就可能不知道名字空间从而产生问题。