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brk(2) [redhat man page]

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

NAME
brk, sbrk - change data segment size SYNOPSIS
#include <unistd.h> int brk(void *end_data_segment); void *sbrk(ptrdiff_t increment); DESCRIPTION
brk sets the end of the data segment to the value specified by end_data_segment, when that value is reasonable, the system does have enough memory and the process does not exceed its max data size (see setrlimit(2)). sbrk increments the program's data space by increment bytes. sbrk isn't a system call, it is just a C library wrapper. 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, and sbrk returns a pointer to the start of the new area. On error, -1 is returned, and errno is set to ENOMEM. CONFORMING TO
BSD 4.3 brk and sbrk are not defined in the C Standard and are deliberately excluded from the POSIX.1 standard (see paragraphs B.1.1.1.3 and B.8.3.3). SEE ALSO
execve(2), getrlimit(2), malloc(3) Linux 0.99.11 1993-07-21 BRK(2)

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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 2.12: _BSD_SOURCE || _SVID_SOURCE || (_XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED) && !(_POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600) Before glibc 2.12: _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED 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 loca- tion of the program break. RETURN VALUE
On success, brk() returns zero. On error, -1 is returned, and errno is set to ENOMEM. (But see Linux Notes below.) 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. Linux notes 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 3.53 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/. Linux 2010-09-20 BRK(2)

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