RE: timings II. const varying vs value varying

I agree Scott.

To return a varying lgth string the called func could ALLOC the bytes needed
and then return a pointer to the allocated varying string data.

 pGetString          b
 dGetString          pi           *
 d pString           s            *
 d String            s         80 a  based( pString ) varying
 c                 eval      pString = %alloc( %size(String))
 c                 eval      String = 'some text to return'
 c                 return    pString
 p                   e

Only problem is insuring the returned pointer is %DEALLOC'd.

now if a DS could have a constructor, destructor and operator member
functions .... :)

Steve Richter



-----Original Message-----
From: rpg400-l-admin@midrange.com [mailto:rpg400-l-admin@midrange.com]On
Behalf Of Scott Klement
Sent: Thursday, October 10, 2002 1:03 AM
To: rpg400-l@midrange.com
Subject: RE: timings II. const varying vs value varying



On Wed, 9 Oct 2002, Steve Richter wrote:
>
> Its just a hunch of mine.  C relies on null term strings so I am
speculating
> that ILE handles them efficiently.
>


Yes, I'm familiar with C, since I program in it on Unix machines.
Normally, though, when you pass a string in C you pass a pointer.  I don't
think I've EVER seen a C function that passes a string by value.

In fact, it's very difficult to pass a string by value in C.  I'm not
evern sure that you CAN without using a data structure...

Normally you'd do something like this:

       int myfunc(const char *input, char *output, int size);

  Which means that the input is a pointer to a null-terminated string,
  passed as "const" (so you can't change it in the function)  the output
  is also a pointer to a null-terminated string.   This would be
  equivalent to the following RPG prototype:

    D myfunc          PR            10I 0
    D  input                          *   value options(*string)
    D  output                         *   value options(*string)
    D  size                         10I 0 value

See? You're passing the strings by pointer, i.e. by reference.  So you
really can't compare it to a varying field passed by value.

To pass by value in C you'd have to do something like:

#include <stdio.h>

struct stuff {
   char mystring[32000];
};

int myfunc(struct stuff t) {
     printf("%s\n", t.mystring);
     return 0;
}

int main(void) {
    struct stuff b;
    strcpy(b.mystring, "This got passed by value!");
    return 0;
}


So, that's about the same thing as:

    D myfunc          PR            10I 0
    D   string                   32000A   value

Even though the string is "variable length" (i.e. null-terminated) in C,
it still copies all 32000 bytes.   So I would expect it to actually be
less efficient than the RPG counterpart.   I suppose I could write up a
benchmark and try it...  but this message is already getting long :)

At any rate, nobody EVER passes strings by value in C.  So, I SERIOUSLY
doubt you'd find it more efficient than RPG.


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