Solved

unix system programming....shmget error

Posted on 2007-11-17
5
2,815 Views
Last Modified: 2013-12-26
Hello experts,

I have a really urgent question. I'm doing a system programming for my os class. When I use shmget function, I get an error saying invalid argument....I don't understand. Can anyone help~~~?

struct mySharedMem{
...
...
}

mySharedMem* shm;                                                            

int main(int argc, char* argv[]){
  mySharedMem* shm;
  int shmId;
  key_t key = KEYVALUE;

  int numProcesses;
  pid_t pid;

  if((shmId = shmget(key, sizeof(mySharedMem), IPC_CREAT|0666)) <0){
    perror("Error in main: shmget");     //I get error message from this line!!!!
    exit(1);                                            // error is "Error in main:shmget: invalid argument"
  }

help~~~
0
Comment
Question by:shinymoon
  • 3
  • 2
5 Comments
 
LVL 12

Accepted Solution

by:
PCableGuy earned 500 total points
ID: 20306356
I think the problem is in this part, what is "key" refer to? Check that first, and correct it if necessary, and report back.

shmget(key, sizeof(mySharedMem), IPC_CREAT|0666)
0
 

Author Comment

by:shinymoon
ID: 20306767
Thanks for responding.

at the begining of my program,  I defined KEYVALUE like below
/#define KEYVALUE 5678

but, I changed my code as your advice and run it again..I get the exactly same error
my code looks like .....

int main(int argc, char* argv[]){
  mySharedMem* shm;
  int shmId;
  key_t key = 5678;

  if((shmId = shmget(key, sizeof(mySharedMem), IPC_CREAT|0666)) <0){
    perror("Error in main: shmget");
    exit(1);
  }

which argument is invalid !?
0
 

Author Comment

by:shinymoon
ID: 20306771
and the error is...
Error in main: shmget: Invalid argument
0
 

Author Comment

by:shinymoon
ID: 20306782
oh, I just tried a different value for key that is 123. It worked. Thanks ^^
Is there any limitation to assign the value for the key???
0
 
LVL 12

Expert Comment

by:PCableGuy
ID: 20307721
Hi shinymoon,

Most of the code I've seen usually uses IPC_PRIVATE as the key. Otherwise, I think you might need to use the ftok function to get a key. In other words, I don't think it can be an arbitrary number. Perhaps, that's a good question for your programming class instructor.

http://www.csl.mtu.edu/cs4411.ck/www/NOTES/process/shm/key.html
0

Featured Post

Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
Looking for Linux Network Interface Card Driver for a 3Com 3C9050 and instructions on how to install 16 86
List out all word 7 259
tripleUp challenge 7 74
MaxSpan challenge 9 80
Here is how to use MFC's automatic Radio Button handling in your dialog boxes and forms.  Beginner programmers usually start with a OnClick handler for each radio button and that's just not the right way to go.  MFC has a very cool system for handli…
In this article, I'll describe -- and show pictures of -- some of the significant additions that have been made available to programmers in the MFC Feature Pack for Visual C++ 2008.  These same feature are in the MFC libraries that come with Visual …
This video will show you how to get GIT to work in Eclipse.   It will walk you through how to install the EGit plugin in eclipse and how to checkout an existing repository.
Along with being a a promotional video for my three-day Annielytics Dashboard Seminor, this Micro Tutorial is an intro to Google Analytics API data.

910 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

20 Experts available now in Live!

Get 1:1 Help Now