sbrk(2) - f31

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);
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13       void *sbrk(intptr_t increment);
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15   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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17       brk(), sbrk():
18           Since glibc 2.19:
19               _DEFAULT_SOURCE ||
20                   (_XOPEN_SOURCE >= 500) &&
21                   ! (_POSIX_C_SOURCE >= 200112L)
22           From glibc 2.12 to 2.19:
23               _BSD_SOURCE || _SVID_SOURCE ||
24                   (_XOPEN_SOURCE >= 500) &&
25                   ! (_POSIX_C_SOURCE >= 200112L)
26           Before glibc 2.12:
27               _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500
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DESCRIPTION

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

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

54       4.3BSD; SUSv1, marked LEGACY in SUSv2, removed in POSIX.1-2001.
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NOTES

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

81       This page is part of release 5.02 of the Linux  man-pages  project.   A
82       description  of  the project, information about reporting bugs, and the
83       latest    version    of    this    page,    can     be     found     at
84       https://www.kernel.org/doc/man-pages/.
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88Linux                             2016-03-15                            BRK(2)