If ampersands aren't needed for function pointers, why does boost::bind require one?

问题

I've always believed that function pointers don't require an ampersand:

Do function pointers need an ampersand

Yet, every example I've seen of using boost::bind shows one, and my compiler - in most situations - gives a typically inscrutable error message if it's omitted.

synchronize(boost::bind(&Device::asyncUpdate , this, "ErrorMessage"));  // Works

synchronize(boost::bind(Device::asyncUpdate , this, "ErrorMessage"));   // Fails

Am I wrong in assuming that boost::bind's first parameter is basically function pointer?

回答1:

Function pointers don't need it, member function pointers do.

Device::asyncUpdate is member function, as you could guess because it is being bound to this.

Here's a normative quote from n3337, 5.3.1/4

A pointer to member is only formed when an explicit & is used and its operand is a qualified-id not enclosed in parentheses.

来源：https://stackoverflow.com/questions/18312186/if-ampersands-arent-needed-for-function-pointers-why-does-boostbind-require