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(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500
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DESCRIPTION

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

35       On success, brk() returns zero.  On error, -1 is returned, and errno is
36       set to ENOMEM.  (But see Linux Notes below.)
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38       On success, sbrk() returns the previous program break.  (If  the  break
39       was  increased,  then this value is a pointer to the start of the newly
40       allocated memory).  On error, (void *) -1 is returned, and errno is set
41       to ENOMEM.
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CONFORMING TO

44       4.3BSD; SUSv1, marked LEGACY in SUSv2, removed in POSIX.1-2001.
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NOTES

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

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

71       This page is part of release 3.22 of the Linux  man-pages  project.   A
72       description  of  the project, and information about reporting bugs, can
73       be found at http://www.kernel.org/doc/man-pages/.
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77Linux                             2008-06-18                            BRK(2)
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