Objects like std::cout and std::cin

[tluisrs]

Hi everyone. I'm new in this forum. I'll try to help anyone I could.

I wanna create 2 objects like std::cout and std::cerr. I've been constructing a log system. I'll write the files here.

//File Log.h
#ifndef _LOG_
#define _LOG_

class Log {
    
    int x;

    Log& operator<< (char* text);

};

#endif

So, I created another file, called LogUtil.h, that contain my objects.

//File LogUtil.h

#ifndef _UTILS_
#define _UTILS_

Log lcout;
Log lcerr;

#endif 

The problem I've got is that when I try to include LogUtil.h twice or more times, I've got the link error that "Log lcout" is already define in another file.

I tried Singleton desing pattern, but I've got the same error. If everyone know how do I solve this problem, please help me.

[jsmith]

Do not instantiate global variables in header files. That results in duplicate symbol link errors.

Your LogUtil.h file should have

extern Log lcout;
extern Log lcerr;

and LogUtil.cpp should instantiate them.

[tluisrs]

Hi jsmith

but when I put on LogUtil.h

extern Log lcout;
extern Log lcerr;

I'll not instaciante then?

[helios]

No. The extern keyword tells the compiler that the symbol being declared is defined in a different file.
It's like when you declare and define a function in two different files, only with variables and objects, extern must be used.