Re: [DUG] Converting some code from C

[Terry]

** is double indirection. Pointer to a pointer.

If you have ...
char * p;
then *p is a char, p is a pointer to a character.

If you have...
 char ** p;
 then **p is a character, *p is a pointer to a character, p is a pointer to a pointer to a character.

All parameters in C are passed by value. So if you want to pass in a var parameter, you need to pass in a pointer to the value to be referenced/modified. But if you want to be able to change where the pointer is pointing from within a function, you need ** (otherwise you just change what the pointer is pointing to).

Terry

Phil Middlemiss wrote:

Thankyou.

 

What does the ** operator in C?

 

Cheers,

Phil.

----- Original Message -----

From: Terry

To: NZ Borland Developers Group - Delphi List

Sent: Monday, April 19, 2004 1:20 PM

Subject: Re: [DUG] Converting some code from C

return exits the function immediately. goto is like the pascal  goto.

Terry


Phil Middlemiss wrote:

 
One more question: The original C source code uses gotos. Does a "return"
statement in C mean just leave the routine, or does it also return back to
the next statement after the goto? I would assume that it does not continue
after a goto statement, but this code is so convoluted I can't be sure what
it intended to do just by looking at the code.

Phil.
----- Original Message ----- 
From: "Terry" <[EMAIL PROTECTED]>
To: "NZ Borland Developers Group - Delphi List" <[EMAIL PROTECTED]>
Sent: Monday, April 19, 2004 12:18 PM
Subject: Re: [DUG] Converting some code from C


  

Pointers and arrays are essentially equivalent in c. And pointer
arithmatic works like array indexation, so ...

*(snorm+n) = *(snorm+n-1)*(float)(2*n-1)/(float)n;

and

snorm[n] = *(snorm+n-1)*(float)(2*n-1)/(float)n;

and

snorm[n] = snorm[n-1]*(float)(2*n-1)/(float)n;

are all equivalent statements.

A reason you may wish to use the pure pointer form is where you don't
want to pass an array and index offset into a function, you can just
point to an element. And p++ will increment the pointer to the next
array element (probably the reason p is used rather than snorm directly).

Terry


Phil Middlemiss wrote:

    

I'm converting some code from some ugly C. The code defines one
      

particular
  

array, and a constant like this:

static float snorm[169];
static float *p = snorm;

and then later has an assignment:

*snorm = 1.0;

and then again later (n is an integer iterator):

*(snorm+n) = *(snorm+n-1)*(float)(2*n-1)/(float)n;

The question is this: It looks like the code is simply assigning values
      

to
  

an array, so why bother with the pointers? Elsewhere the code uses arrays
normally (ie. indexing them with the square brackets) so that makes me
      

think
  

maybe this is doing something other than just putting values into the
      

array.
  

Also, I'm assuming that the "p" variable is just a pointer into snorm?

Can anyone make this clear for me?

Cheers,
Phil.

_______________________________________________
Delphi mailing list
[EMAIL PROTECTED]
http://ns3.123.co.nz/mailman/listinfo/delphi



      

_______________________________________________
Delphi mailing list
[EMAIL PROTECTED]
http://ns3.123.co.nz/mailman/listinfo/delphi

    

_______________________________________________
Delphi mailing list
[EMAIL PROTECTED]
http://ns3.123.co.nz/mailman/listinfo/delphi

  

---

_______________________________________________
Delphi mailing list
[EMAIL PROTECTED]
http://ns3.123.co.nz/mailman/listinfo/delphi

_______________________________________________
Delphi mailing list
[EMAIL PROTECTED]
http://ns3.123.co.nz/mailman/listinfo/delphi
  

_______________________________________________
Delphi mailing list
[EMAIL PROTECTED]
http://ns3.123.co.nz/mailman/listinfo/delphi