Thread: Random number generator

Ok I seem to have a further problem, with the rand function. It produces the same set of random numbers in the same order every time it get's called. Now if I use the srand(time(NULL)) to create a different seed every time. The time function seems to return the same number every time and therefore produce the same random number every time.

Code:

#include <stdlib.h>
char* LB_Random(char *maxR,char *dummy)
	{	
	int i;
	static char n[10];
	int rMax = atoi(maxR);	
	rMax++;
	i = rand() % rMax;
	sprintf(n,"%d",i);
	return n;	
	}

The above produces: 9,3,14,4,1,12,6,14 everytime

Code:

#include <stdlib.h>
char* LB_Random(char *maxR,char *dummy)
	{	
	int i;
	static char n[10];
	int rMax = atoi(maxR);	
	rMax++;
                srand(time(NULL));
	i = rand() % rMax;
	sprintf(n,"%d",i);
	return n;	
	}

Produces the number 5 everytime, due to the time function returning the same number.

srand() should only be called once. Do it outside the function or keep a static boolean variable that knows whether or not srand() has been called.

Ok let me try and explain this a bit better. I'm using a piece of software which will take a C header file and an obj file, import these as extra functionality and then it can call the functions these have defined so it's something like this.

Code:

INCLUDE(random)
while(not_eof)
{
    call(random,"15")
    go to next line
}

The 15 represents the maximum random number, now my header file looks like this

Code:

extern char* LB_Random(char*,char*);

And as you know my main code looks like this

Code:

char* LB_Random(char *maxR,char *dummy)
	{	
	int i;
	static char n[10];
	int rMax = atoi(maxR);	
	rMax++;	
	i = rand() % rMax;
	sprintf(n,"%d",i);
	return n;	
	}

Seeing as you say I can only call srand once ever, what should I do. The only thing i can think of is defining another function in the above code that seeds during initialisation, and then calling the random function over and over. So something like

Code:

//Init
INCLUDE(random)
call(seed,"")
while(not_eof)
{
   call(random,"15")
   go to next line
}

How's that sound.

Yay it works