Passing data structure to another process using shared memory and saving to file
I am sending data(name, ph number & address) to another process using shared memory. I have to print data in the second process and store them to a file. I have tried this code but I am not receiving data in second process. Can someone help me with this. Thank you.
address.c
typedef struct
{
char lname[25];
char fname[20];
char address[20];
char phonenumber[20];
}addressbook;
addressbook a;
char *shared_memory;
int main()
{
int select;
int segment_id;
char* shared_memory;
int segment_size;
key_t shm_key;
const int shared_segment_size = 0x6500;
shm_key = ftok("/home/madan/programs/shm_tok",'C');
if(shm_key < 0) {
printf("failed to create the key %s\n",strerror(errno));
}
/* Allocate a shared memory segment. */
segment_id = shmget (shm_key, shared_segment_size,
IPC_CREAT | IPC_EXCL | S_IRUSR | S_IWUSR);
if(segment_id < 0) {
printf("error geting the segment id %s\n",strerror(errno));
}
printf("segment ID:%d\n", segment_id);
/* Attach the shared memory segment. */
shared_memory = (char*) shmat (segment_id, 0, 0);
printf ("shared memory attached at address %p\n", shared_memory);
printf("enter lastname:\n");
gets(a.lname);
printf("enter firstname:\n");
gets(a.fname);
printf("enter address:\n");
gets(a.address);
printf("enter phone number:\n");
gets(a.phonenumber);
memcpy(shared_memory, &a, sizeof(a));
printf("data:%s\n", shared_memory);
system("./address-insert");
/* Detach the shared memory segment. */
shmdt (shared_memory);
/
* Deallocate the shared memory segment.*/
shmctl (segment_id, IPC_RMID, 0);
}
address-insert.c
typedef struct
{
char lname[20];
char fname[20];
char address[20];
char phonenumber[20];
}addressbook;
addressbook a;
int main ()
{
int segment_id;
char* shared_memory;
FILE *fp;
char *name;
int segment_size;
key_t shm_key;
shm_key = ftok("/home/madan/programs/shm_tok",'D');
const int shared_segment_size = 0x6500;
/* Allocate a shared memory segment. */
segment_id = shmget (shm_key, shared_segment_size,
S_IRUSR | S_IWUSR);
if(segment_id < 0) {
printf("error:[%s]",strerror(errno));
}
printf("segment id %d\n",segment_id);
/* Attach the shared memory segment. */开发者_开发问答
shared_memory = (char*) shmat (segment_id, 0, 0);
if(shared_memory == NULL) {
printf("failed to attach the shared memory %s",strerror(errno));
}
printf ("shared memory2 attached at address %p\n", shared_memory);
printf ("name=%s\n", shared_memory);
memcpy(&a, shared_memory, sizeof(a));
printf("name: %s\n", a.fname);
printf("address:%s\n", a.address);
printf("phone number=%s\n", a.phonenumber);
fp = fopen("filename","a+");
fwrite(a, 1, strlen(a),fp);
fclose(fp);
/* Detach the shared memory segment. */
shmdt (shared_memory);
return 0;
}
Why do you require two processes? If you want to do this you will also need a semaphone - so that the other process can be sure that all the data is in the shared memory. Perhaps a pipe (UNIX or otherwise) would be simpler.
In memcpy(&a, shared_memory, sizeof(a));
instead of passing the size of the variable a
, try passing the size of structure address i.e. sizeof(addressbook)
.
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