Question

I have this class:

Logger.h

class Logger{

    std::string filename;
    std::ofstream fileStream;

    /*Some methods ...*/
};

extern Logger* log;

In another header file i have included the *log definition:

Foo.h

#include "Logger.h"

class Foo{
    Logger* log;

    /*Other code*/
};

But if in Foo.cpp file i try to do this:

log = new Logger();

the compiler give me an error, any idea?

Answer 1

First, variables declared as external must be defined. So you need to have

Logger *log;

in Logger.cpp. You can also initialize it there like this:

Logger *log = new Logger();

Second, you don’t need any more declarations, that is you just need to include Logger.h, no need to declare another Logger variable in Foo.h, just use log from Logger.h.