AT&T C compilers

[Guy Harris]

 >The AT&T C compiler (from System V, Release 2?) chokes on a declaration
 >of the form:
 >
 >extern int bob(double (*)()) ;
 >
 >On the other hand, it is accepted by Microsoft C and other C compilers.

(Deep breath, count to 5)  Prototypes are a relatively new feature in C
implementations.  Some compilers do not support them.  The "Portable C
Compiler", upon which many (most?) UNIX C compilers - including the ones
AT&T supplies - are based, does not support them.

 >The AT&T C++ translator also chokes on this. Is this declaration 
 >incorrect, or have I been bitten by a compiler bug?

Neither.

The declaration in question appears to be correct, except that it says
the argument taken by "bob" is a pointer to a function returning
"double", but doesn't say what sort of arguments that function takes.  I
think this is legal, however.

This does not mean that there is a bug in the AT&T C compiler, though. 
It merely means that the S5R2 C compiler doesn't support function
prototypes.

I don't know whether it's legal C++ or not; if it is, I suspect the
declaration says, in C++, that the function to which the pointer points
takes no arguments (since C++, unlike C, does not have the notion of
"old-style" function declarations where an empty argument list indicates
that the types of the arguments are unknown).