shmdt()--Detach Shared Memory Segment from Calling Process

 #include <sys/shm.h>

 int shmdt(const void *shmaddr);  

The shmdt() function detaches the shared memory segment specified by shmaddr from the calling job. The shmaddr is the value returned by the shmat function.

The system maintains status information about a shared memory segment which can be retrieved with the shmctl() function. When a shared memory segment is successfully detached, the system sets the members of the shmid_ds structure as follows:

• shm_nattch is decremented by 1.

• shm_lpid is set to the process ID of the calling thread.

• shm_dtime is set to the current time.

Parameters

shmaddr

(Input) Address of the shared memory segment to be detached.

Authorities

Authorization Required for shmdt()

Return Value

Error Conditions

If shmdt() is not successful, errno usually indicates one of the following errors. Under some conditions, errno could indicate an error other than those listed here.

[EDAMAGE]

A damaged object was encountered.

The shared memory segment has been damaged by a previous shared memory operation.

[EFAULT]

The address used for an argument is not correct.

In attempting to use an argument in a call, the system detected an address that is not valid.

While attempting to access a parameter passed to this function, the system detected an address that is not valid.

[EINVAL]

The value specified for the argument is not correct.

A function was passed incorrect argument values, or an operation was attempted on an object and the operation specified is not supported for that type of object.

An argument value is not valid, out of range, or NULL.

The value of shmaddr is not the start address of a shared memory segment.

[ENOSYS]

Function not implemented.

An attempt was made to use a function that is not available in this implementation for any object or any arguments.

The function is not implemented.

[EUNKNOWN]

Unknown system state.

The operation failed because of an unknown system state. See any messages in the job log and correct any errors that are indicated, then retry the operation.

Error Messages

None.

Usage Notes

1. This function does not delete the shared memory segment. To delete a shared memory segment, use the shmctl() function with the cmd parameter set to IPC_RMID.

Related Information

• The <sys/shm.h> file (see Header Files for UNIX-Type Functions)
  
  
• shmat()--Attach Shared Memory Segment to Current Process
  
  
• shmctl()--Perform Shared Memory Control Operations
  
  
• shmget()--Get ID of Shared Memory Segment with Key

Example

See Code disclaimer information for information pertaining to code examples.

For an example of using this function, see Using Semaphores and Shared Memory in Examples: APIs.