How to allow a std:string parameter to be NULL?

Question

I have a function foo(const std::string& str); that it does crash if you call it using foo(NULL).

What can I do to prevent it from cras

Answer 1

You could use Boost.Optional.

#include 
#include 

using namespace std;
using namespace boost;

void func(optional& s) {
    if (s) {  // implicitly converts to bool
        // string passed in
        cout << *s << endl; // use * to get to the string
    } else {
        // no string passed in
    }
}

To call it with a string:

string s;
func(optional(s));

and without a string:

func(optional());

Boost.Optional gives you a typesafe way to have nullable values without resorting to pointers and their associated problems.