定义：
#if defined(QT_STATIC_BUILD)
# define QCP_LIB_DECL
#elif defined(QCUSTOMPLOT_COMPILE_LIBRARY)
# define QCP_LIB_DECL Q_DECL_EXPORT
#elif defined(QCUSTOMPLOT_USE_LIBRARY)
# define QCP_LIB_DECL Q_DECL_import
#else
# define QCP_LIB_DECL
#endif
正在属性里面定义C++->preprocessor->中添加QCUSTOMPLOT_COMPILE_LIBRARY
