Aquí está mi configuración ...

/* Bounded Buffer item structure */
struct item {
    int  id;  /* string index value */
    char str[80];  /* string value */
};

/* Structure for the shared memory region */
typedef struct {
    int    debug;           /* debug flag */
    int    in;              /* index of next empty slot */    
    int    out;             /* index of next full slot  */
    char   MUTEXname[32];   /* name of the MUTEX semaphore */
    char   EMPTYname[32];   /* name of the EMPTY semaphore */
    char   FULLname[32];    /* name of the FULL semaphore  */
    struct item buff[BUFFSIZE];  /* circular buffer for producer/consumer items*/
    char   strarray[MAX_STRINGS][80]; /* shared array of strings for consumers */
} shr_mem_t;

/* Values for obtaining a shmid key via ftok() */
#define KEYPATH "."
#define KEYPROJ 4520

Main: (bifurcará () los procesos "Productor" y "Consumidor")

/* Use ftok() to get a value for a key to identify a shared memory segment */
shm_key = ftok(KEYPATH, KEYPROJ);

/* Create the shared memory segment */
shmid = shmget(shm_key, sizeof(shr_mem_t), IPC_CREAT | IPC_EXCL | 0660);

/* Attach shared memory segment to the parent process */
shmptr = shmat(shmid, NULL, 0);

Productor

/* Use ftok() to get value for the key to identify the shared memory segment */
shm_key = ftok(KEYPATH, KEYPROJ);

/* Get the ID of the existing shared memory segment */
shmid = shmget(shm_key, sizeof(shr_mem_t), 0660);

/* Attach the shared memory segment */
shmptr = shmat(shmid, NULL, 0);

Consumidor

/* Use ftok() to get value for the key to identify the shared memory segment */
shm_key = ftok(KEYPATH, KEYPROJ);

/* Get the ID of the existing shared memory segment */
shmid = shmget(shm_key, sizeof(shr_mem_t), 0660);   

/* Attach the shared memory segment */
shmptr = shmat(shmid, NULL, 0);

Pruebas de error: (en aras de la brevedad ...)

if (shmid == -1) {
    perror("shmget failed in __________");
    exit(1);
} else {
    sprintf(errString, "<*> __________ shared memory id: %i ", shmid);
    perror(errString);
}

if(shmptr == (void *)(-1)) {
    perror("shmat failed in __________");
    exit(1);
} else {
    sprintf(errString, "<*> __________ attaching to shared memory address: %p ", shmptr);
    perror(errString);
}

Salida

<*> Main creating shared memory id: 101376 : No such file or directory
<*> Main attaching to shared memory address: 16000 : No such file or directory
Creating the producer and consumer processes...
<*> Producer located shared memory id: 101376 : Successful
<*> Consumer located shared memory id: 101376 : Successful
<*> Producer attaching to shared memory address: 10000 : Successful
<*> Consumer attaching to shared memory address: 10000 : Successful

¿Qué está pasando con la dirección de memoria compartida? ¿Cómo los procesos Main y Prod / Cons obtienen diferentes shmaddr cuando se conectan cuando tienen el mismo shmid?

Gracias por adelantado

Z @ K!