brk(2) - c7

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 2.12:
19               _BSD_SOURCE || _SVID_SOURCE ||
20                   (_XOPEN_SOURCE >= 500 ||
21                       _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED) &&
22                   !(_POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600)
23           Before glibc 2.12:
24               _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 ||
25               _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
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DESCRIPTION

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

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

52       4.3BSD; SUSv1, marked LEGACY in SUSv2, removed in POSIX.1-2001.
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NOTES

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

79       This  page  is  part of release 3.53 of the Linux man-pages project.  A
80       description of the project, and information about reporting  bugs,  can
81       be found at http://www.kernel.org/doc/man-pages/.
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85Linux                             2010-09-20                            BRK(2)