Did you change the sizeof? You don't even use buffer in the first program, so you can get rid of that. Then when you shmget pass (sizeof(int) * 2) as the size argument.
Also, to the third argument, shmflg, you have to OR in IPC_CREAT. So the call should be:
Code:
key_t shmkey=0x200;
int id;
..,
id = shmget(shmkey, sizeof(int) * 2, 0666 | IPC_CREAT);
Without IPC_CREAT, it's likely that shmget is returning -1 which, since you're not doing error checking, is then passed to shmat which is returning NULL. When you attempt to reference through the NULL pointer you are seg faulting.
I suggest reading the man pages for shmget!
edit: I also suggest not using 0666 and using the proper mode flags; but that's your prerogative. For example:
Dear Reader,
Is is necessary to attach / dettach the shared memory segments for write operations , if more than one program is accessing same shared memory segments..
I have used semaphore mutex and still I'm getting segmentation fault when I write to the segment when other program is already... (1 Reply)
I am running HP-UX B.11.11.
I'm increasing a parameter for a database engine so that it uses more memory to buffer the disk drive (to speed up performance). I have over 5GB of memory not being used.
But when I try to start the DB with the increased buffer parameter I get told.
"Not... (1 Reply)
Hi all :confused: ,
I am new to unix.I have been asked to implement shared memory in user's mode.What does this mean?What is the difference it makes in kernel mode and in users mode?What are the advantages of this impemenation(user's mode)?
And also i would like to know why exactly shared... (0 Replies)
what i want to do is have an int that can been written into by 2 processes but my code doesn't seem to work.
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <sys/shm.h>
#include<stdio.h>
#define KEY1 (1492)
int main()
{
int shmid;
volatile int * addr;... (6 Replies)
hi,
this is the problem: i want to swap a linked list between 4 processes (unrelated), is there any way i can do that just by sending a pointer to a structure?
//example
typedef struct node
{
int x;
char c;
struct node *next;
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or i should send the items ( x,c ) by... (9 Replies)
I need to create a shared library to access an in memory DB. The DB is not huge, but big enough to make it cumbersome to carry around in every single process using the shared library. Luckily, it is pretty static information, so I don't need to worry much about synchronizing the data between... (12 Replies)
I am writing a shared library in Linux (but compatible with other UNIXes) and I want to allow multiple instances to share a piece of memory -- 1 byte is enough. What's the "best" way to do this? I want to optimize for speed and portability.
Obviously, I'll have to worry about mutual exclusion. (0 Replies)
Hello.
I am new to this forum and I would like to ask for advice about low level POSIX programming.
I have to implement a POSIX compliant C shared library.
A file will have some variables and the shared library will have some functions which need those variables.
There is one special... (5 Replies)
Discussion started by: iamjag
5 Replies
LEARN ABOUT HPUX
shm_unlink
shm_unlink(2) System Calls Manual shm_unlink(2)NAME
shm_unlink - unlink a shared memory object
SYNOPSIS DESCRIPTION
The system call removes the name of the shared memory object named by the string pointed to by name. If one or more references to the
shared memory object exists when the object is unlinked, the name will be removed before returns, but the removal of the memory object con-
tents will be postponed until all open and map references to the shared memory object have been removed.
RETURN VALUE
returns the following values:
Successful completion.
Failure,
is set to indicate the error.
ERRORS
If fails, is set to one of the following values:
[EACCES] Permission to unlink the named shared memory object is denied.
[ENAMETOOLONG] The length of the name string exceeds or the length of a (pathname) component of the name string exceeds while is in
effect.
[ENOENT] The named shared memory object does not exist.
[ENOSYS] is not supported by the implementation.
SEE ALSO shm_open(2), close(2), mmap(2), munmap(2), privileges(5).
STANDARDS CONFORMANCE shm_unlink(2)
12-16-2011
where i find manual of mode flags?