What’s the use of multiple asterisks in the function call?

One of the standard conversions, in both C and C++, is the function-to-pointer conversion; when a function name appears in an expression, it can be converted into a pointer to that function. So:

• foo is equivalent to &foo
• *foo is equivalent to *(&foo), or foo
• **foo is eqivalent to **(&foo), or *foo, or foo

and so on.

This means that you can legally add as many * as you like before a function name without changing its meaning. There’s no reason to do that, though.