Overloading << operator C++ - Pointer to Class

Question

class logger {
 ....
};

logger& operator<<(logger& log, const std::string& str)
{
    cout << "My Log: " << str << endl;
    return log;
}

logger log;
log << "Lexicon Starting";

Works fine, but i would like to use a pointer to a class instance instead. i.e.

logger * log = new log();
log << "Lexicon Starting";

Is this possible? If so what is the syntax? Thanks

Edit: The compiler Error is

error: invalid operands of types 'logger*' and 'const char [17]' to binary 'operator<<'

Answer 1

You'd have to dereference the pointer to your logger object and obviously check if it's not 0. Something like this should do the job:

  log && ((*log) << "Lexicon starting")

As a general aside, I would shy away from referencing objects like a logger (which you normally unconditionally expect to be present) via a pointer due to the uncertainty you get with a pointer, AKA is there an object or not?

Answer 2

Here is the way:

logger * log = new log();
(*log) << "Lexicon Starting";

Answer 3

Why not use a reference?

logger & log = *(new log()); 
// the above is abhorrent code that 
// should be replaced by something meaningful

log << "Lexicon Starting";

if this isn't what you want I'd go with Timo Geusch, even if it is ugly

Answer 4

Depending on the context where you get your logger from, you might want to return a reference instead of a pointer:

...
Logger& logger() {
    return *_pLogger;
}
...

Logger& log = logger();
log << "...";

Answer 5

Not really. new log( ) has pointer type, "Lexicon starting" has type const char[16]. You can only overload operators if at least one argument has a user-defined type.

decasteljau correctly remarked that you could do this via (*log), if you wanted the pointer. I don't like the pointer, however. Andrei Alexandrescu devotes quite a few pages on smart logger singletons in "Modern C++ Design", might be worth to consult that.