Shared memory between two c program

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LEARN ABOUT OPENDARWIN

shmget

SHMGET(2)						      BSD System Calls Manual							 SHMGET(2)

NAME

     shmget -- get shared memory area identifier

SYNOPSIS

     #include <sys/types.h>
     #include <sys/ipc.h>
     #include <sys/shm.h>

     int
     shmget(key_t key, int size, int shmflg);

DESCRIPTION

     shmget() returns the shared memory identifier associated with the key key.

     A shared memory segment is created if either key is equal to IPC_PRIVATE, or key does not have a shared memory segment identifier associated
     with it, and the IPC_CREAT bit is set in shmflg.

     If a new shared memory segment is created, the data structure associated with it (the shmid_ds structure, see shmctl(2)) is initialized as
     follows:

     o	 shm_perm.cuid and shm_perm.uid are set to the effective uid of the calling process.

     o	 shm_perm.gid and shm_perm.cgid are set to the effective gid of the calling process.

     o	 shm_perm.mode is set to the lower 9 bits of shmflg.

     o	 shm_lpid, shm_nattch, shm_atime, and shm_dtime are set to 0

     o	 shm_ctime is set to the current time.

     o	 shm_segsz is set to the value of size.

RETURN VALUES

     Upon successful completion a positive shared memory segment identifier is returned.  Otherwise, -1 is returned and the global variable errno
     is set to indicate the error.

ERRORS

     [EACESS]		A shared memory segment is already associated with key and the caller has no permission to access it.

     [EEXIST]		Both IPC_CREAT and IPC_EXCL are set in shmflg, and a shared memory segment is already associated with key.

     [ENOSPC]		A new shared memory indentifier could not be created because the system limit for the number of shared memory identifiers
			has been reached.

     [ENOENT]		IPC_CREAT was not set in shmflg and no shared memory segment associated with key was found.

     [ENOMEM]		There is not enough memory left to created a shared memory segment of the requested size.

SEE ALSO

     shmctl(2), shmat(2), shmdt(2)

BSD
								  August 17, 1995							       BSD

Programming