Declare the callback function in C ++

When using SNMP ++ to develop network management software, you need to send request packets asynchronously. You need to register a callback function in the function, specifically: typedef void (* snmp_callback) (INT reason, SNMP * Session, PDU & PDU, snmptarget & target, void * data), starts to declare the callback function as a private member in the form of void getcallback (INT reason, SNMP * session, PDU & PDU, snmptarget & target, void * data); but it is always saved during compilation. The error message "unresolved overloaded function type" is displayed. : <, I have carefully checked the return values and parameters of the function and found no problems. It has been plagued for a long time. Later, I found that the callback function in C ++ cannot be declared as a non-static member of the class, because the non-static member function will add the this pointer to the parameter during compilation, the parameter list will change, so we should Static functions declared as global functions or classes.