How to create functions like std::cout?

Question

I\'m creating my own logging utility for my project, I want to create a function like iostream\'s std::cout, to log to a file and print to the console as well.

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Answer 1

You could define an enum like

enum loglevel_en {
    log_none, log_debug, log_info, log_waring, log_error };

then have a global variable:

enum loglevel_en my_log_level;

and provide some way to set it (e.g. from program arguments).

At last, define a macro (in a global header)

#define MY_LOG(Lev,Thing) do { if (my_log_level >= Lev) \
    std::cout << __FILE__ << ":" << __LINE__ \
              << " " << Thing << std::endl; } while(0)

and use it like

 MY_LOG(log_info, "x=" << x)

Feel free to improve MY_LOG macro to output more things (date, etc...)

You could define instead

#define LOG(Lev) if (my_log_level >= Lev) std::cout 

but that does not play nice with code like

if (x>34)
  LOG(log_info) << "strange x=" << x;
else return;

So I strongly suggest something like MY_LOG