Name
getpagesize — get memory page size
Synopsis
#include <unistd.h>
int
getpagesize( |
void); |
![[Note]](../stylesheet/note.png) |
Note | ||
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DESCRIPTION
The function getpagesize()
returns the number of bytes in a page, where a "page" is the
thing used where it says in the description of mmap(2) that files are
mapped in page-sized units.
The size of the kind of pages that mmap(2) uses, is found using
#include <unistd.h> long sz = sysconf(_SC_PAGESIZE);
(most systems allow the synonym _SC_PAGE_SIZE for _SC_PAGESIZE), or
#include <unistd.h> int sz = getpagesize();
CONFORMING TO
SVr4, 4.4BSD, SUSv2. In SUSv2 the getpagesize() call is labeled LEGACY, and
in POSIX.1-2001 it has been dropped; HP-UX does not have this
call. Portable applications should employ sysconf(_SC_PAGESIZE) instead
of this call.
NOTES
Whether getpagesize() is
present as a Linux system call depends on the architecture.
If it is, it returns the kernel symbol PAGE_SIZE, whose value depends on the
architecture and machine model. Generally, one uses binaries
that are dependent on the architecture but not on the machine
model, in order to have a single binary distribution per
architecture. This means that a user program should not find
PAGE_SIZE at compile time from
a header file, but use an actual system call, at least for
those architectures (like sun4) where this dependency exists.
Here libc4, libc5, glibc 2.0 fail because their getpagesize() returns a statically derived
value, and does not use a system call. Things are OK in glibc
2.1.