Question

I am having a problem getting this COMPARE macro to work. Any ideas on how to fix?

Its a bit of an artificial sample – I wanted to make it as small as possible.

#include <iostream>
#include <string.h>

enum rqtypes {Unknown, Monitor, Query, Snapshot };

class base {
public:
   base() : type(Unknown) {}
   rqtypes type;
};

class CBMonitorDeviceRequest : public base
{
public:
   CBMonitorDeviceRequest() : dn(0) {}
   char* dn;
};


//I want the equivalent of:
//        case MonitorDeviceRequestID:
//           CBMonitorDeviceRequest* pthis = static_cast<CBMonitorDeviceRequest*>(thisrq);
//           if(pthis && strcmp(pthis->dn1, "1234") == 0)
//              return 0;
//           else
//              return -1;
//           break;


int main(int argc, char* argv[])
{
   CBMonitorDeviceRequest* ptr = new CBMonitorDeviceRequest;
   ptr->type = Monitor;
   ptr->dn = new char(strlen("1234") + 1);
   strcpy(ptr->dn, "1234");

#define COMPARE(id, thismsg) case id##ID: { \
   CB##id * pthis = static_cast<CB##id *>(thismsg); \
   if(pthis && strcmp(pthis->dn, "1234") == 0) \
      std::cout << "found"; \
   else \
      std::cout << "not found"; \
     break;  } \

   switch(ptr->type){
      COMPARE(Monitor, ptr);
   }

#undef COMPARE

    return 0;
}

I get eg:

(46) : error C2065: 'MonitorID' : undeclared identifier
(46) : error C2051: case expression not constant
(46) : error C2065: 'CBMonitor' : undeclared identifier
(46) : error C2065: 'pthis' : undeclared identifier
(46) : error C2061: syntax error : identifier 'CBMonitor'
(46) : error C2065: 'pthis' : undeclared identifier
(46) : error C2065: 'pthis' : undeclared identifier
(46) : error C2227: left of '->dn' must point to class/struct/union/generic type

Using gcc -E I get:
# 30 “macro_fun2.cpp”
int main(int argc, char* argv[])
{
CBMonitorDeviceRequest* ptr = new CBMonitorDeviceRequest;
ptr->type = Monitor;
ptr->dn = new char(strlen(“1234”) + 1);
strcpy(ptr->dn, “1234”);
# 45 “macro_fun2.cpp”
switch(ptr->type){
case MonitorID: { CBMonitor * pthis = static_cast(ptr); if(pthis && strcmp(pthis->dn, “1234”) == 0) Monitor = Query; else Monitor = Snapshot;
break; };
}

return 0;
}

*** By the way I changed code to to avoid the massive printing of iostream by preprocessor - otherwise -E printing would have been huge.

#define COMPARE(id, thismsg) case id##ID: { \
   CB##id * pthis = static_cast<CB##id *>(thismsg); \
   if(pthis && strcmp(pthis->dn, "1234") == 0) \
      id = Query; \
   else \
      id =  Snapshot; \
     break;  } \

Answer 1

id##ID will expand to MonitorID, which isn’t defined. You either want to rename Monitor to MonitorID in the definition of rqtypes, or change this to just id.

CB##id will expand to CBMonitor, which also isn’t defined. You either want to rename class CBMonitorDeviceRequest to class CBMonitor, or change this to CB##id##DeviceRequest.

Apart from that, I can’t see any obvious problems. Apart from the memory leak, of course. Why aren’t you using std::string for your strings?