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man:sbrk

BRK(2) Linux Programmer's Manual BRK(2)

NAME

     brk, sbrk - change data segment size

SYNOPSIS

     #include <unistd.h>
     int brk(void *addr);
     void *sbrk(intptr_t increment);
 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
     brk(), sbrk():
         Since glibc 2.19:
             _DEFAULT_SOURCE ||
                 (_XOPEN_SOURCE >= 500) &&
                 ! (_POSIX_C_SOURCE >= 200112L)
         From glibc 2.12 to 2.19:
             _BSD_SOURCE || _SVID_SOURCE ||
                 (_XOPEN_SOURCE >= 500) &&
                 ! (_POSIX_C_SOURCE >= 200112L)
         Before glibc 2.12:
             _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500

DESCRIPTION

     brk()  and  sbrk()  change  the  location  of  the program break, which
     defines the end of the process's data segment (i.e., the program  break
     is the first location after the end of the uninitialized data segment).
     Increasing the program break has the effect of allocating memory to the
     process; decreasing the break deallocates memory.
     brk()  sets the end of the data segment to the value specified by addr,
     when that value is reasonable, the system has enough  memory,  and  the
     process does not exceed its maximum data size (see setrlimit(2)).
     sbrk() increments the program's data space by increment bytes.  Calling
     sbrk() with an increment of 0 can be used to find the current  location
     of the program break.

RETURN VALUE

     On success, brk() returns zero.  On error, -1 is returned, and errno is
     set to ENOMEM.
     On success, sbrk() returns the previous program break.  (If  the  break
     was  increased,  then this value is a pointer to the start of the newly
     allocated memory).  On error, (void *) -1 is returned, and errno is set
     to ENOMEM.

CONFORMING TO

     4.3BSD; SUSv1, marked LEGACY in SUSv2, removed in POSIX.1-2001.

NOTES

     Avoid  using  brk() and sbrk(): the malloc(3) memory allocation package
     is the portable and comfortable way of allocating memory.
     Various systems use various types for the argument of  sbrk().   Common
     are int, ssize_t, ptrdiff_t, intptr_t.
 C library/kernel differences
     The  return value described above for brk() is the behavior provided by
     the glibc wrapper function for the Linux brk() system call.   (On  most
     other  implementations,  the  return value from brk() is the same; this
     return value was also specified in SUSv2.)  However, the  actual  Linux
     system  call returns the new program break on success.  On failure, the
     system call returns the current break.  The glibc wrapper function does
     some  work  (i.e.,  checks  whether the new break is less than addr) to
     provide the 0 and -1 return values described above.
     On Linux, sbrk() is implemented as a library  function  that  uses  the
     brk()  system  call,  and does some internal bookkeeping so that it can
     return the old break value.

SEE ALSO

     execve(2), getrlimit(2), end(3), malloc(3)

COLOPHON

     This page is part of release 4.16 of the Linux  man-pages  project.   A
     description  of  the project, information about reporting bugs, and the
     latest    version    of    this    page,    can     be     found     at
     https://www.kernel.org/doc/man-pages/.

Linux 2016-03-15 BRK(2)

/data/webs/external/dokuwiki/data/pages/man/sbrk.txt · Last modified: 2019/05/17 09:47 by 127.0.0.1

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