Hi,

Sorry to confuse you with the coding. I added the header file and made a few changes. I am not an expert in programming.

Server Code

#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
const int SHM_SIZE = 1024; /* make it a 1K shared memory segment */
//const char FILE_NAME[] = "ser1.c";

int main(int argc, char *argv[])
{
key_t key;
int shmid;
int n;
FILE *fileptr;
char *stop="stop";
char data[1000];
fileptr=fopen("test1.txt","w");
char *shmflag,*shm;
int flag=0;
// Make the key 
if ((key = ftok("/Home/r/rameshnn/OS/A2/ser1.c", 1)) == -1) {
perror("ftok");
exit(1);

}

/* connect to (and possibly create) the segment: */
if ((shmid = shmget(key, SHM_SIZE, 0644 | IPC_CREAT)) == -1) {
perror("shmget");
exit(1);
}

/* attach to the segment to get a pointer to it: */
shm = shmat(shmid, (void *)0, 0);
if (shm == (char *)(-1)) {
perror("shmat");
exit(1);
}

/* attach to the segment to get a pointer to it: */ // FLAG POINTER
shmflag = shmat(shmid, (void *)0, 0);
if (shmflag == (char *)(-1))
{
perror("shmat");
exit(1);
}



while(shmflag==0)
{
sleep(1);
} 


while(flag==0)
{
fprintf(fileptr,shm);

if(strcmp("stop\n",shm) != 0 ) 
{
flag=0;
} 
else
{
flag=1;

} 

}

fclose(fileptr);


/* detach from the segment: */
if (shmdt(shm) == -1) {
perror("shmdt");
exit(1);
}

/* delete the IPC structure */
shmctl(shmid, IPC_RMID, NULL);


//exit(0);
return 0;
}

Client Code

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

const int SHM_SIZE = 1024; /* make it a 1K shared memory segment */
//const char FILE_NAME[] = "ser1.c";

int main(int argc, char *argv[])
{
key_t key;
int shmid;
int flag=0;
// FILE *fileptr;
char name[1000];
//fileptr=fopen("test.txt","w");
char *shmflag,*shm;
// shm=fileptr; 

// Make the key 
if ((key = ftok("/Home/r/rameshnn/OS/A2/ser1.c", 1)) == -1) {
perror("ftok");
exit(1);

}

/* connect to (and possibly create) the segment: */
if ((shmid = shmget(key, SHM_SIZE, 0644 | IPC_CREAT)) == -1) {
perror("shmget");
exit(1);
}
/* attach to the segment to get a pointer to it: */
shm = shmat(shmid, (void *)0, 0);
if (shm == (char *)(-1))
{
perror("shmat");
exit(1);
}

/* attach to the segment to get a pointer to it: */ // FLAG POINTER
shmflag = shmat(shmid, (void *)0, 0);
if (shmflag == (char *)(-1))
{
perror("shmat");
exit(1);
}


shmflag=0;

// Write with first character "*"
printf("write to segment: \n");


while(flag==0)
{

fgets(shm, SHM_SIZE, stdin);
//*shm=*shm+1;

if(strcmp("stop\n",shm) == 0)
{
flag=1;
} 
}

shmflag=1;


exit(0);
return 0;
}

It is looping infintely and printing only the first line of the input. We have to execute the server program first and then client program. When we type "stop" in a new line both programs should stop and the text which was typed before stop should be printed in test1.txt.