Assume in 1.txt file ,i have saved 32
writer.c
-----------
reader.c
---------
Can any body pls tell me why am i not able to retrieve the correct value in reader.c?shmid & key values are same in both the programs.Where i went wrong?Any help is very appreciable?
Moderator's Comments:
Use code tags please, see PM.
Last edited by zaxxon; 07-29-2013 at 08:36 AM..
Reason: code tags
There are quite a few things wrong with both the reader and writer programs...however the one thing that jumps out is that both the read and write calls expect a pointer as their 2nd argument...while you are providing an int** pointer...so once the 2nd argument to read and write is made an int* type then it should work...
As shamrock said, there were several things wrong with both reader.c and writer.c. You might try the following replacements for them:
reader.c:
writer.c:
Run:
to build them. A file named writer must exist for reader to be able to access the shared memory segment created by writer. If you run reader before you run writer, reader will fail because the shared memory segment hasn't been created yet. (You may want to try this to see what happens.)
When writer runs, it creates the shared memory segment (if it doesn't already exist); then it writes a string into the segment and prints the string it wrote to stdout before exiting.
You can use the command ipcs -ma to see all of the active shared memory segments on your system. Each time you rebuild writer the inode number of the file named writer may change; if it does, the next run of writer will create a new shared memory segment instead of using the previously created segment. (This is a "feature" of the way ftok() works.)
The reader program can be run any number of times you want and it will show you the current contents of the shared memory segment. The writer program can also be run any number of times and each run will update the string stored in the shared memory segment.
You can remove a shared memory segment using the command:
You can find a shared memory segment's ID and Key from the output of the ipcs command given above and from the output of the reader and writer commands given in this message.
This was tested on Mac OS X running on a MacBook Pro laptop, but should work on any system that provides the shared memory features first developed for UNIX System III and now required on all UNIX branded systems. It is also required on POSIX conforming systems that claim to support the X/Open System Interfaces extension option.
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)
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)
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)
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;
} node;
or i should send the items ( x,c ) by... (9 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 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)
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)
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)