|SHMAT(3P)||POSIX Programmer's Manual||SHMAT(3P)|
void *shmat(int shmid, const void *shmaddr, int shmflg);
The shmat() function attaches the shared memory segment associated with the shared memory identifier specified by shmid to the address space of the calling process. The segment is attached at the address specified by one of the following criteria:
- If shmaddr is a null pointer, the segment is attached at the first available address as selected by the system.
- If shmaddr is not a null pointer and (shmflg &SHM_RND) is non-zero, the segment is attached at the address given by (shmaddr -((uintptr_t)shmaddr %SHMLBA)). The character '%' is the C-language remainder operator.
- If shmaddr is not a null pointer and (shmflg &SHM_RND) is 0, the segment is attached at the address given by shmaddr.
- The segment is attached for reading if (shmflg &SHM_RDONLY) is non-zero and the calling process has read permission; otherwise, if it is 0 and the calling process has read and write permission, the segment is attached for reading and writing.
Otherwise, the shared memory segment shall not be attached, shmat() shall return (void *)-1, and errno shall be set to indicate the error.
- Operation permission is denied to the calling process; see Section 2.7, XSI Interprocess Communication.
- The value of shmid is not a valid shared memory identifier, the shmaddr is not a null pointer, and the value of (shmaddr -((uintptr_t)shmaddr %SHMLBA)) is an illegal address for attaching shared memory; or the shmaddr is not a null pointer, (shmflg &SHM_RND) is 0, and the value of shmaddr is an illegal address for attaching shared memory.
- The number of shared memory segments attached to the calling process would exceed the system-imposed limit.
- The available data space is not large enough to accommodate the shared memory segment.
The following sections are informative.
The Base Definitions volume of POSIX.1‐2017, Section 3.346, Shared Memory Object, <sys_shm.h>
Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .
|2017||IEEE/The Open Group|