gdb breakpoint on base class, but failed - mongodb

Question

in mongodb, class cursor is defined as 'Cursor : boost::noncopyable', and then there are many class which are derived from it. I want to know for a given operation from client, which XXXCursor was used. so I want to set a breakpoint on Cursor::Cursor. but failed.
(gdb) b mongo::Cursor::Cursor
the class mongo::Cursor does not have any method named Cursor
Hint: try 'mongo::Cursor::Cursor<TAB> or 'mongo::Cursor::Cursor<ESC-?>
(Note leading single quote.)
Make breakpoint pending on future shared library load? (y or [n]) n
(gdb) ptype mongo::Cursor
type = class mongo::Cursor : private boost::noncopyable_::noncopyable {
public:
~Cursor(int);
virtual bool ok(void);
bool eof(void);
virtual mongo::Record * _current(void);
virtual mongo::BSONObj current(void);
virtual mongo::DiskLoc currLoc(void);
virtual bool advance(void);
virtual mongo::BSONObj currKey(void) const;
....
}
(gdb) list mongo::Cursor::Cursor
**the class mongo::Cursor does not have any method named Cursor
Hint: try 'mongo::Cursor::Cursor<TAB> or 'mongo::Cursor::Cursor<ESC-?>**
(Note leading single quote.)
But I wrote a similar program
#include <iostream>
#include <boost/utility.hpp>
class Base : boost::noncopyable {
public:
void printx() {std::cout<< getx() <<"\n" ;}
virtual int getx()=0;
};
class P : public Base {
public:
int x;
virtual int getx() { return x*3;}
P(int c){ x= c;}
};
int main(){
P p(2);
p.printx();
return 0;
}
I can set breakpoint on Base::Base sucessfully.
do you have any idea why I can't set breakpoint on mongo::Cursor::Cursor ?
mongo::Cursor was definied here: https://github.com/mongodb/mongo/blob/master/src/mongo/db/cursor.h

Answer 1

As for your example. If I compile it like this:
g++ -O0 -g -m64 -I ./boost_1_53_0 main.cpp
I can set a breakpoint on Base::Base and I see Base::Base as a symbol:
>nm -C a.out | grep Base::Base
0000000000400a4e W Base::Base()
If I compile compile it like this (with optimization level O2):
g++ -O2 -g -m64 -I ./boost_1_53_0 main.cpp
I don't see Base::Base as a symbol:
>nm -C a.out | grep Base::Base
>
And can't set a breakpoint:
(gdb) b Base::Base
the class Base does not have any method named Base
Hint: try 'Base::Base<TAB> or 'Base::Base<ESC-?>
So as a first step make sure that there is mongo::Cursor::Cursor as a symbol in your program or shared library. It can be optimized out.