use of D.Knuth pseudo-random generator

Question

I need to write a physical simulation software, and I need to use the pseudo-random generator written by D.Knuth, cause it best fits my needs.

Though I know how to use it within a hard block of code (a mere #include "rng-double.c"), I can't quite understand how to include it in a modular program where it is needed both within the main and inside some libraries that I then link back into the main through header files.

The only functions that I need are ranf_start(seed) to seed the generator and ranf_arr_next() to generate the next number.

I'm getting a long series of

multiple definitions of 'foo'

pretty much for every function that is defined in the random number generator code.

I'm not an expert, so I find myself pretty much at a dead end. Is there a way out? I am currently trying to write an header file for the rng, though I haven't been successful yet.

Thanks a lot, everybody. ~J

EDIT: From what the first answers say, I need to wirte the header file. I did it for most functions in the generator, but I cant manage to write it right for the function that actually generates the number. How should I write the header for a function defined like this?

#define ranf_arr_next() (*ranf_arr_ptr>=0? *ranf_arr_ptr++: ranf_arr_cycle())

score 5 · Answer 1 · answered Oct 17 '10 at 16:50

5

You don't include the .c file, but the appropriate header file, which contains the declarations of your functions. The .c file will just be compiled along with the rest.

answered Oct 17 '10 at 16:50

Eiko

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score 2 · Answer 2 · answered Oct 17 '10 at 16:55

If you ever find yourself #including a .c file, then chances are that you are doing something wrong. You really should be #including .h files only.

This wikipedia link explains exactly the problem you are having and how to write the header file properly.

I suspect your problem is that you are not using the header 'guard' properly.

Jonathan Leffler · Accepted Answer · 2010-10-17T20:57:35.203

rng-double.h

#ifndef RNG_DOUBLE_H_INCLUDED
#define RNG_DOUBLE_H_INCLUDED

extern void ranf_start(long seed);
extern double ranf_next(void);

#ifdef USE_MACRO_RANF_NEXT
extern double *ranf_arr_ptr;
extern double  ranf_arr_cycle(void);
#define ranf_arr_next() (*ranf_arr_ptr >= 0 ? *ranf_ptr++ : ranf_arr_cycle())
#endif /* USE_MACRO_RANF_NEXT */

#endif /* RNG_DOUBLE_H_INCLUDED */

main.c

#include "rng-double.h"
...other stuff...

rng-double.c

#define USE_MACRO_RANF_NEXT
#include "rng-double.h"

double *ranf_arr_ptr;

void ranf_start(long seed)
{
    ...implementation...
}

double (ranf_next)(void)  // Function
{
    ranf_next();          // Macro
}

double ranf_arr_cycle(void)
{
    ...implementation...
}

I got rid of the ranf_next function, since I didn't want to modify the original source, if possible. In practice, I moved the whole macro into the header. Thanks for the precious hints though. By the way, in the code you proposed there is a type errors (ranf_start eats long's). — japs, Oct 17 '10 at 19:16

use of D.Knuth pseudo-random generator

3 Answers3

rng-double.h

main.c

rng-double.c

Linked