Re re: declaring routines which return function pointers

Graham Bromley graham at orca.UUCP
Tue Dec 18 03:15:54 AEST 1984

> I have a routine which resembles the following:
> 	int (*f)();
> 	int fa(), fb();
> 	fa() {
> 		f = fb;
> 		return(f);
> 	}
> 	fb() {
> 	}
> The problem with the above is that lint complains about an 
> illegal combination of a pointer with an integer in the 
> 'return' statement.  I have tried various casts and function 
> declarations to try to satisfy lint, but none of them have 
> worked.  Does anybody know what I should do to keep lint happy?

>> I played around with the code for about 30 minutes and the only 
>> thing I accomplished was to make lint core dump twice.  I only 
>> see one way of doing it and C apparently doesn't support it.  
>> That way is to declare fa() as:
>>  int ((*fa)())();
>> This is broken down from:
>> int  (*x)();	/* x is a pointer to a function returning an int */
>> int ((*y)())();	/* y is function returning a ptr to a func returning an int */
>> However, both lint and cc complain with 'function returns illegal 
>> type'. May I suggest using casts?

	No no no! The only problem here is incorrect usage of C syntax.
You want to declare a function returning a pointer to an integer
function. Build up the type declaration as you say it:
1.  fa is a function               fa()
2.  returning a pointer to         *fa()
3.  an integer                     int *fa()
4.  function                       int (*fa())()
You need the () around *fa() in step 3. because the () operator is
evaluated left to right.
    If this is too confusing (function pointer syntax is rarely
crytal clear) use a typedef:
typedef int (*IFPTR)();     /* int func ptr */
IFPTR   fa();               /* func returning ptr to int func */
    To call fa then the function whose address is returned by 
fa, say:
    (*fa(a1, a2, ...))(b1, b2, ...)
where the a1 etc are fa's arguments, and the b1 etc. are the
arguments of the function whose address is returned by fa.
Or you could say:
    int (*f)();
    f = fa(a1, a2, ...);
    (*f)(b1, b2, ...);
if you want to remember the function pointer returned by fa.

    gbgb, aka the longjmp artist (an unfair alias)

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