Shared memory program

Hi,

I have one requirement to store an array of structure at shared memory. Also the shared memory should have one counter to store number of elements in the array.

I tried to look at some placed but didn't find anything relevant.

So my first question, is it possible that we can store two things on same shared memory. And second if not then how to achieve the same?

Thanks

Hello,

> I tried to look at some placed but didn't find anything relevant.

Well, if you try "<your platform> shared memory" I'm sure you can find something relevant.

As for your constraint, yes, you can store whatever you want, but if it's easier for you, define a structure holding both a counter and an array of those sub-structures you talk about.

Quote:

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Originally Posted by maven

I have one requirement to store an array of structure at shared memory. Also the shared memory should have one counter to store number of elements in the array.

---

You can write a struct which meets these requirements. Then you can share a pointer to the struct with any function that needs access to it.

ok.

I tried it like this. Used below structure and struct "forShm" to insert in shared memory. I am able to copy data and do all. But while reading seems it is getting some garbage. I believe i messed up something.

Code:

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typedef struct userList
{
  char userName[64];
  int  socketFd;
  int  gpReady;
}listUsers;

struct forShm
{
  listUsers userInfo[10];
  int  numUsers;
  int  numGpUsers;
};

            shmid = shmget((key_t)1234, sizeof(struct forShm)*10, 0666 | IPC_CREAT);
            sh_mem = shmat(shmid, (void *)0, 0);
            fromShm = (struct forShm*)sh_mem;

            strcpy(fromShm->userInfo[count].userName,tokName);
            fromShm->userInfo[count].socketFd = sockfd;
            count=count+1;
            fromShm->numUsers = count;

---

Post the part of your code that is reading and that you believe is wrong.
Also I may misunderstand something but why sizeof(struct forShm)*10 ? you already have your 10 users in 1 forShm structure.

@maven:
8 years on this board, 134 posts, you should have enough experience under your belt to do a little research on your own, and read some documentation. Nevertheless, here's some help:
Let me google that for you
shm_overview(7) - Linux man page
shmat(2): shared memory operations - Linux man page
shmget(2): allocates shared memory segment - Linux man page

Notice that all the shared memory functions return some sort of error information and set errno. Try actually checking for errors, and printing useful error messages (e.g. using perror()) if they fail. And obviously, if your shared memory functions fail, exit your program with an error.