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brk(2)
NAME
  brk, sbrk - Change space allocation

SYNOPSIS
  #include <unistd.h>

  int brk(
	  void *addr );

  void *sbrk(
	  intptr_t incr );

  The following function prototypes do not conform to current standards and
  are supported only for backward compatibility:

  int brk(
	  char *addr );

  void *sbrk(
	  ssize_t incr );

  void *sbrk(
	  long incr );

LIBRARY
  Standard C Library (libc)

STANDARDS
  Interfaces documented on this reference page conform to industry standards
  as follows:

  brk(), sbrk(): XSH4.2

  Refer to the standards(5) reference page for more information about
  industry standards and associated tags.

PARAMETERS
  addr
      Points to the effective address of the maximum available data.

  incr
      Specifies the number of bytes to be added to the current break. The
      value of incr may be positive or negative.

DESCRIPTION
  The brk() function sets the lowest data segment location not used by the
  program (called the break) to addr.

  In the alternate function sbrk(), incr more bytes are added to the
  program's data space, and a pointer to the start of the new area is
  returned.

  When a program begins execution with the execve() function, the break is
  set at the highest location defined by the program and data storage areas.
  Therefore, only programs with growing data areas should need to use sbrk().

  The current value of the program break is reliably returned by the call
  sbrk(0). The getrlimit() function may be used to determine the maximum
  permissible size of the data segment. It is not possible to set the break
  beyond the value returned from a call to the getrlimit() function.

  If the data segment was locked at the time of the brk() function,
  additional memory allocated to the data segment by brk() will also be
  locked.

NOTES
  Programmers should be aware that the concept of a current break is a
  historical remnant of earlier UNIX systems. Many existing UNIX programs
  were designed using this memory model, and these programs typically use the
  brk() or sbrk() functions to increase or decrease their available memory.

  The use of the mmap() function is now preferred because it can be used
  portably with all other memory allocation functions and with any function
  that uses other allocation functions.

RETURN VALUES
  Upon successful completion, the brk() function returns a value of 0 (zero),
  and the sbrk() function returns the prior break value. If either call
  fails, a value of -1 is returned and errno is set to indicate the error.

ERRORS
  If the brk() or sbrk() function fails, no additional memory is allocated
  and errno is set to one of the following values:

  [EINVAL]
	  [Tru64 UNIX]	Indicates an attempt to set a break value to less
	  than the initial value at program startup.

  [ENOMEM]
	  The requested change would allocate more space than allowed by the
	  limit as returned by the getrlimit() function.

SEE ALSO
  Functions: exec(2), getrlimit(2), mmap(2), plock(2), malloc(3)

  Standards: standards(5)

Index for Section 2

Alphabetical listing for B

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