Shared Memory Communication

#include <stdio.h>

#include <stdlib.h>

#include <sys/mman.h>

#include <sys/stat.h>

#include <fcntl.h>

#include <string.h>

struct DataExchange {

    int i1;

    int i2;

};

int main(int argc, char **argv)

{

    struct DataExchange *pRead, *pWrite;

    char sSharedMemReadName[100] = "_CODESYS_SharedMemoryTest_Write"; 

    char sSharedMemWriteName[100] = "_CODESYS_SharedMemoryTest_Read";

    int fdRead = shm_open(sSharedMemReadName, O_CREAT | O_RDWR, S_IRWXU | S_IRWXG);

    printf("Shared Memory Read: %s %d\n\n",sSharedMemReadName, fdRead);

    ftruncate(fdRead, sizeof(*pRead));

    pRead = mmap(0, sizeof(*pRead), PROT_READ | PROT_WRITE, MAP_SHARED, fdRead, 0);

    close(fdRead);

    int fdWrite = shm_open(sSharedMemWriteName, O_CREAT | O_RDWR, S_IRWXU | S_IRWXG);

    printf("Shared Memory Write: %s %d\n\n",sSharedMemWriteName, fdWrite);

    ftruncate(fdWrite, sizeof(*pWrite));

    pWrite = mmap(0, sizeof(*pWrite), PROT_READ | PROT_WRITE, MAP_SHARED, fdWrite, 0);

    close(fdWrite);

    do

    {

        sleep(1);

        printf("pRead->i1: %d pRead->i2: %d pWrite->i1: %d pWrite->i2: %d\n", 

               pRead->i1, pRead->i2, pWrite->i1, pWrite->i2);

        printf("Press 'Enter' to increment values or 'q' and then 'Enter' to quit\n");    

        pWrite->i1++;

        pWrite->i2--;     

    } while (getchar() != 'q');

    munmap(pRead, sizeof(*pRead));

    shm_unlink(sSharedMemReadName);

    munmap(pWrite, sizeof(*pWrite));

    shm_unlink(sSharedMemWriteName); 

    exit(0);

}