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Mapping a struct instance to shared memory

Posted on 2003-03-12
Medium Priority
Last Modified: 2013-12-26

I'm rather weak in C and my knowledge of IPC is lacking as well so I'd appreciate any and all advice.

The problem:

I'm writing a program in C that allocates shared memory for interprocess communication. So I shmget it and shmat it and end up with a pointer to this shared memory block (please feel free to correct me if I'm wrong.)

Now I have a structure defined by

typedef struct something{
int a;
int b;
char c[100];
int d;
} something2;

and I want an instance of this struct to be placed in the shared memory so that I could use something2_instance.a from any process that has access to this shared memory block...

Maybe something along the lines of creating a pointer to the struct instance and .. then doing something to it?

As you see I'm really puzzled, any hints?

THank you in advance
Question by:NeverAgain

Accepted Solution

akshayxx earned 400 total points
ID: 8124528
first of all have a look on this link.. its a very good tutorial..

and about mapping the struct to shared memory..well here is the way ( using the definition of ur struct)

void *shm;
something2 *s1;

now lets say u get pointer to the memory with
shm=shmat(..usual stuff);

now there are at least two basic ways to fill the value of struct at shm
1)  make a something2 variable fill up and copy to memory at shm
fill up s1  ..
s1->a=12;... and so on..


2) typecast the shm to something2 * and fill up the values;

s1->a=12; s1->b=24;  and so on

this will write only one something2 type data on shm .. u can extend it to put array of structs and more stuff..
also when writer is writing .. reader shud wait .. and viceversa .. the usual synchronization stuff

Author Comment

ID: 8124608

I'll give it a try

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