Any way to forward declare a function prototype?

[jsyjr]

I make regular use of forward class declarations and pointers to such classes.

I now have a need to pass a function pointer through a number of layers. I would prefer to include the header that declares my function pointer's prototype only into the module that dereferences a function pointer rather than into each layer that simply passes along that pointer value.

Is this possible?

[Banfa]

A function declaration is a forward declaration in so far as it does not define a function only declares it as existing in the same way a class forward declaration only declares the existence of a class and does not define it.

[jsyjr]

You misunderstood my question. I am not asking about declaring a function. I am looking for the analog of a forward class declaration. I can write:

class foo;

void bar(foo*);

void waz(foo* p)
{
bar(p);
}

Notice that waz knows nothing about class foo other than its name. Perhaps bar will have access to foo's complete description. Perhaps bar will simply pass p further along. Who cares? Only those sites that dereference a foo* pointer. All others can write "class foo;" and be done.

Similarly I know that I can write:

typedef void foo(int, double);

void bar(foo*);

void waz(foo* p)
{
bar(p);
}

The difference is that in this case the identifier foo not only is known to denote a function type but further includes the full prototype. This forces me into one of two unpleasant scenarios:

1) clone the typedef at multiple sites (yuck! fragile!)
2) stick the typedef in a header and include it everywhere the function pointer type is mentioned.

Notice the asymetry: in the case of a data object I only needed to provide a complete description of class foo at those points where I want to dereference a foo*.

[Banfa]

Notice the asymetry: in the case of a data object I only needed to provide a complete description of class foo at those points where I want to dereference a foo*.

No I notice it being exactly the same, in both the case of the function and the class you only have to provide a declaration of it in order to use a pointer to it. In neither case do you have to provide the definition in order to use a pointer.

Yes the declaration of a function is more complex than the declaration of a class.

[jkmyoung]

Go with option 2, the header, for consistency and maintenance reasons

[jsyjr]

Banfa: I think the answer is that, unlike classes, functions allow overloading so a naked symbol is insufficient.

jkmyoung: I agree. I never seriously considered choosing option 1.