Shared Data Example

How to share the data between two program.

Program 1:
=======
#include<iostream.h>
#include<sys/wait.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include<unistd.h>
#include <stddef.h>
#include <stdio.h>
#define SHMSZ    1024
int write(int *b){
char c;
int shmid;
key_t key;
int *shm;
char *s;
/*    * We'll name our shared memory segment    * "5678".    */
key = 5678;
/*    * Create the segment.    */
if ((shmid = shmget(key, SHMSZ, IPC_CREAT | 0666)) < 0) {
cerr<<"shmget";        exit(1);
}
/*    * Now we attach the segment to our data space.    */
if ((shm = (int *)/*(char *)*/shmat(shmid, 0, 0)) == /*(char *)*/(int *) -1) {
cerr<<"shmat";        exit(1);
}
/*    * Now put some things into the memory for the    * other process to read.    */
// s = shm;
int i;
for (i=0; i<=1000; i++,shm++)
*shm = i;    *b=0;
cout<<"write is complited"<<endl;
cout<<*b<<endl;
return(*b);
}

main(){
char c;
int shmid;
key_t key;
static int *b;
key = 5679;
/*    * Create the one bit  segment.    */
if ((shmid = shmget(key, 1, IPC_CREAT | 0666)) < 0) {
cerr<<"shmget";
exit(1);
 }

/*    * Now we attach the segment to our data space.    */

if ((b = ( int *)shmat(shmid, 0, 0)) == (int *) -1)

{

cerr<<"shmat";

exit(1);    }

cout<<*b<<endl;

int *w=new int;

*w=10;

//while(1)    {

if(*b==1)

{

write(b);

}

else

wait(w);

//}

}

Prgram 2:

======

#include<iostream.h>

#include <sys/types.h>

#include <sys/ipc.h>

#include <sys/shm.h>

#include<unistd.h>

#include<sys/wait.h>

#define SHMSZ    1024

int read(int *b){

char c;

int shmid;

key_t key;

int *shm;

char *s;

/*    * We'll name our shared memory segment    * "5678".    */

key = 5678;

/*    * Create the segment.    */

if ((shmid = shmget(key, SHMSZ, IPC_CREAT | 0666)) < 0) {

cerr<<"shmget";

exit(1);

}

/*    * Now we attach the segment to our data space.    */

if ((shm = (int *)shmat(shmid, 0, 0)) == (int *) -1) {

cerr<<"shmat";

exit(1);

}

/*now read what the server put in the memory.    */

int i;

for (i=0; i<=1000; i++,shm++)

cout<<*shm<<endl;

cout<<"read is completed"<<endl;

*b=1;

cout<<"*b is "<<*b<<endl;

return(*b);

}

main(){

char c;

int shmid;

key_t key;

static int *b;

key = 5679;

/*    * Create the one bit  segment.    */

if ((shmid = shmget(key, 1, IPC_CREAT | 0666)) < 0) {

cerr<<"shmget";

exit(1);

}

/*    * Now we attach the segment to our data space.    */

if ((b = (int *)shmat(shmid, 0, 0)) == (int *) -1) {

cerr<<"shmat";

exit(1);

}

cout<<" *b is "<<*b<<endl;

int *w=new int;

*w=10;

while(1)

{

if(*b==0)

{

read(b);

}

else

wait(w);

}

}