shmget problem

This is a discussion on shmget problem within the C Programming forums, part of the General Programming Boards category; Good evening, I'm trying to allocated share memory and i get the error sh.c: In function `main': sh.c:14: error: parse ...

  1. #1
    g_p
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    shmget problem

    Good evening,

    I'm trying to allocated share memory and i get the error

    sh.c: In function `main':
    sh.c:14: error: parse error before ';' token

    My program is like that :

    Code:
    #define SHMSZ 40;
    
    int main() {
    
    key_t key;
    int shmid;
    
    if((key = ftok("path of user", 0)) < 0){
    printf("\n%d Error in key\n",key);
    return 0;
    }
    
    printf("%d\n",key);
    
    
    shmid = shmget(key,SHMSZ,(IPC_CREAT | 0666));
    
    /* the error appears here inside shmget*/
    
    }
    What do i do wrong?
    Thanks, in advance!

  2. #2
    MFC killed my cat! manutd's Avatar
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    Where is shmget() declared?
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  3. #3
    g_p
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    Well, i have included the libraries :

    #include <sys/types.h>
    #include <sys/ipc.h>
    #include <sys/shm.h>
    #include <stdio.h>
    #include<time.h>
    #include <unistd.h>

  4. #4
    and the hat of wrongness Salem's Avatar
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    Well putting a ; on the end of your #define is usually the wrong thing to do.

    Your use expands to
    shmid = shmget(key,40;,(IPC_CREAT | 0666));
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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  5. #5
    g_p
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    Unbelievable!
    This was the error and I have spent 1 and a half hour to see what was going wrong and it was only a ';'!
    Thanks very much!

  6. #6
    g_p
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    Divide a shared memory segment

    Goodd evening,

    I would like to ask you sthg as far as dividing a shared memory segment into
    8 buffers is concerned.

    e.g. in the following code , we have allocated the shared memory segment and we want now to divide it into 8 stacks which every stack is going to consist of 4 integers.(4 * 8 =32 integers)
    How do we do that?

    Code:
    #include <sys/types.h>
    #include <sys/ipc.h>
    #include <sys/shm.h>
    #include <stdio.h>
    #include<time.h>
    #include <unistd.h>
    
    #define SHMSZ 8
    
    int main() {
    
    key_t key;
    int shmid;
    int *buf;
    
    if((key = ftok("path of user", 0)) < 0){
    printf("\n%d Error in key\n",key);
    return 0;
    }
    
    printf("%d\n",key);
    
    
    shmid = shmget(key,SHMSZ * sizeof(int),(IPC_CREAT | 0666));
    
    
    buf = shmat(shmid,NULL,0);
    
    
    }
    Thanks, in advance!

  7. #7
    Fear the Reaper...
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    Isn't that just taking a 32*sizeof(int) block of memory and dividing it into 8 ? Aka having one pointer point to the beginning of the block, another 4 integers further, and then another 4 integers further, and so on ?
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  8. #8
    g_p
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    Quote Originally Posted by Happy_Reaper
    Isn't that just taking a 32*sizeof(int) block of memory and dividing it into 8 ? Aka having one pointer point to the beginning of the block, another 4 integers further, and then another 4 integers further, and so on ?
    Well,i need to have for every buffer 3 semaphores which are going to check if the buffer is full,empty or no other process tries to have access to this buffer,this means that i must have 8 * 3 = 24 semaphores.

    Do you have any idea how i can utilise that?

    Thanks, in advance!

  9. #9
    Fear the Reaper...
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    Right, you can do that in similar fashion, either in a seperate block or by making your original block bigger by 24 * sizeof(semaphore).
    Teacher: "You connect with Internet Explorer, but what is your browser? You know, Yahoo, Webcrawler...?" It's great to see the educational system moving in the right direction

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