sbrk(2) - f35

1BRK(2)                     Linux Programmer's Manual                    BRK(2)
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NAME

6       brk, sbrk - change data segment size
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SYNOPSIS

9       #include <unistd.h>
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11       int brk(void *addr);
12       void *sbrk(intptr_t increment);
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14   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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16       brk(), sbrk():
17           Since glibc 2.19:
18               _DEFAULT_SOURCE
19                   || ((_XOPEN_SOURCE >= 500) &&
20                       ! (_POSIX_C_SOURCE >= 200112L))
21           From glibc 2.12 to 2.19:
22               _BSD_SOURCE || _SVID_SOURCE
23                   || ((_XOPEN_SOURCE >= 500) &&
24                       ! (_POSIX_C_SOURCE >= 200112L))
25           Before glibc 2.12:
26               _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500
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DESCRIPTION

29       brk()  and  sbrk()  change the location of the program break, which de‐
30       fines the end of the process's data segment (i.e., the program break is
31       the  first  location  after the end of the uninitialized data segment).
32       Increasing the program break has the effect of allocating memory to the
33       process; decreasing the break deallocates memory.
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35       brk()  sets the end of the data segment to the value specified by addr,
36       when that value is reasonable, the system has enough  memory,  and  the
37       process does not exceed its maximum data size (see setrlimit(2)).
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39       sbrk() increments the program's data space by increment bytes.  Calling
40       sbrk() with an increment of 0 can be used to find the current  location
41       of the program break.
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RETURN VALUE

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

53       4.3BSD; SUSv1, marked LEGACY in SUSv2, removed in POSIX.1-2001.
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NOTES

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

80       This page is part of release 5.12 of the Linux  man-pages  project.   A
81       description  of  the project, information about reporting bugs, and the
82       latest    version    of    this    page,    can     be     found     at
83       https://www.kernel.org/doc/man-pages/.
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87Linux                             2021-03-22                            BRK(2)