Tic tac toe using shared memory with SYS V IPC

LinaBellus · 12-13-2018, 01:49 AM

Hey everyone.

I have some trouble finishing my first shared memory game. It's meant to play the well known Tic Tac Toe game between two processes. On the game board 1 stands for X's and 2 stands for O's.

Here's my first program:

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>

#include "header.h"


// function checks whether current player (process) won
int won(Table t)
{
	if (t.matrix[1] > 0) {
		if ((t.matrix[1] == t.matrix[2]) && (t.matrix[1] == t.matrix[3]))
			return 1;
		else
			if ((t.matrix[1] == t.matrix[4]) && (t.matrix[1] == t.matrix[7]))
			return 1;
			else
				if ((t.matrix[1] == t.matrix[5]) && (t.matrix[1] == t.matrix[9]))
				return 1;
	}
	if (t.matrix[9] > 0) {
		if ((t.matrix[9] == t.matrix[8]) && (t.matrix[9] == t.matrix[7]))
			return 1;
		else
			if ((t.matrix[9] == t.matrix[6]) && (t.matrix[9] == t.matrix[3]))
				return 1;
	}
	return 0;

}

//deletes shared memory
void removeshm(int shmid)
{
  	shmctl(shmid, IPC_RMID, NULL);
    printf("Shared memory deleted.\n");
}

//prints gameboard
void print_table(Table t)
{
	int i, j;
	printf("The board: \n");
	for (i=0; i < t.rows; i++) {
	    for (j=0; j < t.columns; j++) {
			printf("%d ",t.matrix[i * t.columns + j]);
	    }
		 printf("\n");
	}
	printf("\n");
}

int main(int argc, char *argv[])
{
	if( argc != 1 )
	{
		printf("Error: no parameter needed!\n");
		exit(0);
  	}
//for details, check header
	Table t;
	t.key = 100;
	t.rows = 3;
	t.columns = 3;

	t.matrix[10] = 0;

//connecting to shared memory
	int shmid = shmget(t.key, 9 * sizeof(int), IPC_CREAT | 0666);
	if (shmid == -1) {
			printf("Existing shared memory. \n");
		}
	else
		printf("Creating new shared memory \n");

	if ((t.matrix = shmat(shmid, NULL, 0)) == (void *) -1) {
			perror("Some error!");
			exit(1);
		}

	srand(getpid());

	while(1) {
//during even steps it's the turn of current player 
		if (t.matrix[10] % 2 == 0) {
			int pos = rand() % (9 - 1) + 1;
//player chooses a free field on the gameboard (field with value of zero) 
			 while (t.matrix[pos] != 0)
				 pos = rand() % (9 - 1) + 1;
			t.matrix[pos] = 1;
			t.matrix[10]++;
			printf("No. of current step: %d \n", t.matrix[10]);
			 print_table(t);
			if (won(t) == 1) {
				t.matrix[10] = 10;
				break;
			}
		}
		printf("\n\n");
		sleep(5);
		if (t.matrix[10] >= 9)
			break;
	}

	removeshm(100);
removeshm(shmid);
}

Second program:

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>

#include "header.h"

int won(Table t)
{
	if (t.matrix[1] > 0) {
		if ((t.matrix[1] == t.matrix[2]) && (t.matrix[1] == t.matrix[3]))
			return 1;
		else
			if ((t.matrix[1] == t.matrix[4]) && (t.matrix[1] == t.matrix[7]))
			return 1;
			else
				if ((t.matrix[1] == t.matrix[5]) && (t.matrix[1] == t.matrix[9]))
				return 1;
	}
	if (t.matrix[9] > 0) {
		if ((t.matrix[9] == t.matrix[8]) && (t.matrix[9] == t.matrix[7]))
			return 1;
		else
			if ((t.matrix[9] == t.matrix[6]) && (t.matrix[9] == t.matrix[3]))
				return 1;
	}
	return 0;

}

void removeshm(int shmid)
{
  	shmctl(shmid, IPC_RMID, NULL);
    printf("Shared memory deleted.\n");
}

void print_table(Table t)
{
	int i, j;
	printf("Board: \n");
	for (i=0; i < t.rows; i++) {
	    for (j=0; j < t.columns; j++) {
			 printf("%d ",t.matrix[i * t.columns + j]);
	    }
		printf("\n");
	}
	printf("\n");
}

int main(int argc, char *argv[])
{
	if( argc != 1 )
	{
		printf("ERROR: no parameter needed!\n");
		exit(0);
  	}


	Table t;
	t.key = 100;
	t.rows = 3;
	t.columns = 3;

int shmid = shmget(t.key, 9 * sizeof(int), IPC_EXCL);

	t.matrix = shmat(shmid, NULL, 0);

	while(1) {
//during odd steps it's the turn of second player 
	if (t.matrix[10] % 2 == 1) {
		int pos = rand() % (9 - 1) + 1;
		while (t.matrix[pos] != 0)
				pos = rand() % (9 - 1) + 1;
		 t.matrix[pos] = 2;
		t.matrix[10]++;
		 printf("No. of current step: %d \n", t.matrix[10]);
		 print_table(t);
		if (won(t) == 1) {
				t.matrix[10] = 10;
				break;
					}
	}
	sleep(5);
	if (t.matrix[10] >= 9)
				break;
	}
	shmdt(t.matrix);
	removeshm(100);
	removeshm(shmid);
}

Also, my header file contains the following:

Code:

typedef struct{
	int rows;
	int columns;
	key_t key;
	int *matrix;
}Table;

My problem is that both server and client stop with segmentation fault, and I don't know why. Program prints the gameboard at each step, but it won't stop once someone has won.
Could someone help me with this?

Thank you in advance.

NevemTeve · 12-13-2018, 02:33 AM

If you wish to use element matrix[10], then change the allocation size to 11*sizeof(int)

Also add more debug-printf, and after every printf use fflush(stdout).

Also pos should be between 1 and 9: pos = rand() % 9 + 1

LinaBellus · 12-13-2018, 03:03 AM

Quote:

Originally Posted by NevemTeve

If you wish to use element matrix[10], then change the allocation size to 11*sizeof(int)

Also add more debug-printf, and after every printf use fflush(stdout).

Also pos should be between 1 and 9: pos = rand() % 9 + 1

Thank you, I fixed that, but program stops at step no. 8 when there's only one free field left so I have to kill processes with CTRL + C.

Also, after editing and recompiling, the program won't even start the game, it stops with message "Creating new shared memory".

EDIT:
Okay, program seems to exit after 9 steps (when gameboard has no free fields left) and deletes shared memory segment, but it won't exit sooner in case one of the players wins.

LinaBellus · 12-13-2018, 04:29 AM

Okay, I fixed it, it works well now. The problem was firstly with the print_table function, both loops must start from 1 and not 0, and a few other smaller issues.