There is no global definition in the header file.

Since a header file may be included more than once, there is a global definition of a redefinition error in the link//global definition should not be placed in the header file, it should be placed in its corresponding implementation file. If the global definition in a header file is used by multiple CPP files, only one file can include this header file, and the other can only be extern these global declarations. #ifndef lock_h#define lock_hvoid LOCK (), void unlock (), void Quanju () {};/////////Caution int quanjubianliang;////be careful class Xiao {void sfkdjsldjfk () {int i;} Class, of course ok! }; #endif

There is no global definition in the header file.