Qt 生成库

1，将原有TARGET（目标）改成如下(e.g.)
TARGET = Demo

改：

Debug:TARGET = Demod
Release:TARGET = Demo

2，TEMPLATE = app 改 lib

3,再加入：DEFINES += DEMO_LIBRARY \

4,再在.h里面加入
#if defined(Demo_LIBRARY)
#  define Demo_EXPORT Q_DECL_EXPORT
#else
#  define Demo_EXPORT Q_DECL_IMPORT
#endif

class Demo_EXPORT CLASS
{
};