🚀 go-pugleaf

In article <C0CAtI.KqM@knot.ccs.queensu.ca> alastair@hecate.phy.queensu.ca  
(A.B. McLean) writes:
> POINTERS TO FUNCTIONS IN METHOD DEFINITIONS
> 
> I want to write a method that will accept a pointer to a C function.
> For example, let the function be a simple Gaussian:-
> 
> void gaussian(x,a,y)
> float x,a[],*y;
> {
>   float arg;
>   
>   arg = (x-a[2])/a[3];
>   *y += a[1]*exp(-arg*arg);
> }
> 
> In the interface file I would expect (Kernigham amd Ritchie section 5.11)
> the method definition to look like 
> 
> - methodName:void(*gaussian)(float, float*, float*);
> 
> and in the implementation file I may have
> 
> - methodName:void(*gaussian)(float, float*, float*)
> {
>   // ...
>   return self;
> }
> 
> When I try to do this the compiler gives me the message
> 
>   parse error before `void'
>   
> Any suggestions ?
> 
> Alastair McLean
> alastair@hecate.phy.queensu.ca

This should do it:

- methodName:(void (*) (float, float*, float*)) gaussian
{
	return self;
}

Hope this works for you, I just tried this:

- doit : (void (*) (int, int)) foo :(int) x :(int) y
{
	// do something
}

in some obj-c code and it worked.

Remember, the syntax for declaring parameters to obj-c methods is different  
than declaring parameters for C functions, objc uses a "cast"-like syntax for  
parameter declarations in methods.

-- 

--- Gordie Freedman gordie@cyclesoft.com  NeXTMail Yes! ---
>>> Thou shalt not inline functions more complicated than 20 

alastair@hecate.phy.queensu.ca (A.B. McLean) writes:
> I want to write a method that will accept a pointer to a C function.


I would guess that this isn't directly possible; it looks like the Objective-C  
runtime doesn't have the ability to encode data of type function pointer.

A couple of solutions might include passing the function pointer as an int  
pointer and then casting it to a function pointer, or to remove the function  
interface and pass a selector:

- invokeThisMethod:(SEL) aMethod
{
	[self perform: aMethod with:self];

}

If aMethod = @selector(foo:), this is roughly equivalent to [self foo:self].

-sam
--
Opinions expressed herein are not those of my employer.  They're not even
mine.  They're probably wrong besides.  How did they get in here, anyway?

In article <C0CAtI.KqM@knot.ccs.queensu.ca> alastair@hecate.phy.queensu.ca  
(A.B. McLean) writes:
> POINTERS TO FUNCTIONS IN METHOD DEFINITIONS
> 
> I want to write a method that will accept a pointer to a C function.
> For example, let the function be a simple Gaussian:-
> 
> void gaussian(x,a,y)
> float x,a[],*y;
> {
>   float arg;
>   
>   arg = (x-a[2])/a[3];
>   *y += a[1]*exp(-arg*arg);
> }
> 
> In the interface file I would expect (Kernigham amd Ritchie section  
5.11)
> the method definition to look like 
> 
> - methodName:void(*gaussian)(float, float*, float*);
> 
> and in the implementation file I may have
> 
> - methodName:void(*gaussian)(float, float*, float*)
> {
>   // ...
>   return self;
> }
> 
> When I try to do this the compiler gives me the message
> 
>   parse error before `void'
>   
> Any suggestions ?
> 
> Alastair McLean
> alastair@hecate.phy.queensu.ca

Thanks to everyone who replied to my pointer to a function problem. 
Here is a summary of the replies:-the syntax given below works..
I tried them !
_______________________________________________________

No, types of arguments to Objective C methods are not specified in the
same way as types of arguments to regular C functions.  Rather, they are
specified in C "cast" format -- e.g., -method:(int)i; not -method:int i;

For your example:

- methodName:(void(*)(float, float*, float*))functionName;

-- 
Ray Spalding
ray.spalding@oit.gatech.edu (NeXT Mail accepted)
________________________________________________________

The syntax for specifying a function pointer is wrong.  Try the following:

- methodName: (void (*)(float, float*, float*))gaussian;

Or, even better

typedef  void (*GaussianFunc)(float, float*, float*);

- methodName: (GaussianFunc)gaussian;


--
Frank Mitchell
frank@fnbc.com (NeXTmail)
________________________________________________________

The best solution might be that to use "typedef".  Simply, you define
a GaussianType as:

typedef void (*GaussianType)(float, float *, float *);

and then declare

- mothodName : (GaussianType) handler
{
 // ...
 return self;
}

and that will do.

ken
zhao@acsc.com
________________________________________________________
Try

- methodName:(void (*gaussian)(float, float*, float*)));

Perhaps this will work (types have to be in parenthesis).

Marcel
waldvoge@nessie.cs.id.ethz.ch (Marcel Waldvogel)
________________________________________________________
Thanks 
Alastair McLean
alastair@hecate.phy.queensu.ca

In article <C0CAtI.KqM@knot.ccs.queensu.ca> alastair@hecate.phy.queensu.ca  
(A.B. McLean) writes:
> I want to write a method that will accept a pointer to a C function.
[...]
> In the interface file I would expect (Kernigham amd Ritchie section 5.11)
> the method definition to look like 
> 
> - methodName:void(*gaussian)(float, float*, float*);

In Objective-C method declarations, all types must be given in parenthesis,  
using the C type-cast syntax.  Also, the name of the argument is given after  
its type.  So what you want is:

- methodName:(void(*)(float, float*, float*))gaussian;

--
Dwight Everhart          "Technology turned out to be less important than
Houston, Texas            sales and distribution methods ... we consistently
biff@biff.gbdata.com      outsold people who had better technology."
NeXTMail and MIME OK      -- Thomas J. Watson Jr., on the success of IBM