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NAME

       getpagesize - get memory page size

SYNOPSIS

       #include <unistd.h>

       int getpagesize(void);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       getpagesize():
           Since glibc 2.12:
               _BSD_SOURCE ||
                   !(_POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600)
           Before glibc 2.12:
               _BSD_SOURCE || _XOPEN_SOURCE >= 500 ||
               _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED

DESCRIPTION

       The function getpagesize() returns the number  of  bytes  in  a  memory
       page,  where  "page"  is  a  fixed-length  block,  the  unit for memory
       allocation and file mapping performed by mmap(2).

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.

NOTES

       Portable applications should employ  sysconf(_SC_PAGESIZE)  instead  of
       getpagesize():

           #include <unistd.h>
           long sz = sysconf(_SC_PAGESIZE);

       (Most systems allow the synonym _SC_PAGE_SIZE for _SC_PAGESIZE.)

       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.

SEE ALSO

       mmap(2), sysconf(3)

COLOPHON

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