Linux Shared Memory C | shmget Example

Linux Shared Memory C | shmget Example

05:24

Description: Following c language program is a Linux shared memory example. This is useful in understanding Linux IPC (Inter process communication). The command/function that is used in this code and can be used in doing shared memory programming is shmget()

#include<stdio.h>

#include<sys/shm.h>

#include<sys/stat.h>

#include<unistd.h>

int count=1;

int main(){

    int segment_id_1,segment_id_2;

    char *shared_memory_1,*shared_memory_2;

    struct shmid_ds shmbuffer;

    int segment_size;

    const int shared_segment_size=0x6400;

    /*Allocate a shared memory segment*/

   

    segment_id_1=shmget (IPC_PRIVATE,shared_segment_size,IPC_CREAT|    IPC_EXCL|S_IRUSR|S_IWUSR);

    segment_id_2=shmget (IPC_PRIVATE,shared_segment_size,IPC_CREAT|    IPC_EXCL|S_IRUSR|S_IWUSR);

    /*Attach the shared memory segment*/

    shared_memory_1=(char*)shmat(segment_id_1,0,0);

    shared_memory_2=(char*)shmat(segment_id_2,0,0);

   

    pid_t pid;

    pid=fork();

    if(pid>0){

       /*Write a string to the shared memory segment*/
       sprintf(shared_memory_1,"Hello Child.");

      

       wait(NULL);

       /*Print out the string from shared memory*/
       printf("Message for Parent: %s\n",shared_memory_2);

       pid_t pid;

       pid=fork();

       if(pid>0){

           wait(NULL);

           printf("Message for Parent: %s\n",shared_memory_2);

           pid_t pid;

           pid=fork();  

           if(pid>0){

              wait(NULL);

              printf("Message for Parent: %s\n",shared_memory_2);

           }

           else if(pid==0){

              /*Print out the string from shared memory*/

              printf("Message for Child#3: %s\n",shared_memory_1);

             

              /*Write a string to the shared memory segment*/

              sprintf(shared_memory_2,"Hello Parent from Chid#3");

      

           }  

       }

       else if(pid==0){

           /*Print out the string from shared memory*/

           printf("Message for Child#2: %s\n",shared_memory_1);

      

           /*Write a string to the shared memory segment*/

           sprintf(shared_memory_2,"Hello Parent from Child#2");

       }                

    }

      

    else if(pid==0){

     

       /*Print out the string from shared memory*/

       printf("Message for Child#1: %s\n",shared_memory_1);

      

       /*Write a string to the shared memory segment*/

       sprintf(shared_memory_2,"Hello Parent from Child#1");

    }
    return 0;

}