shmdt

Purpose

     Detaches a shared memory segment.

Syntax

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

     int shmdt (shmaddr)
     char *shmaddr;

Description

     The shmdt  system call  detaches, from the  calling proc-
     ess's data segment, the  shared memory segment located at
     the address specified by the shmaddr parameter.

     Mapped file  segments are automatically detached  when no
     longer in  use.  However,  you can  use the  shmdt system
     call to  explicitly release the segment  register used to
     map a  file.  Shared  memory segments must  be explicitly
     detached with shmdt.

Return Value

     Upon successful completion, a value of 0 is returned.  If
     shmdt fails, a  value of -1 is returned and  errno is set
     to indicate the error.

Diagnostics

     The shmdt system call fails and the shared memory segment
     is not detached if the following is true:

     EINVAL     The shmaddr parameter is  not the data segment
                start address of a shared memory segment.

     ETXTBSY    The shmdt  system call  attempted to  detach a
                segment attached to a shared library.

Related Information

     In  this book:   "exec:   execl,  execv, execle,  execve,
     execlp,   execvp,"  "exit,   _exit,"  "fclear,"   "fork,"
     "fsync," "shmat," "shmctl," and "shmget."