sbrk(2) [osf1 man page]

brk(2)								System Calls Manual							    brk(2)

NAME

       brk, sbrk - Change space allocation

LIBRARY

       Standard C Library (libc.so, libc.a)

SYNOPSIS

       #include <unistd.h>

       int brk(      void *addr );

       void *sbrk(	intptr_t incr );

       The following function definitions 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 );

STANDARDS

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

       brk(), sbrk():  XPG4-UNIX

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

PARAMETERS

       Points  to the effective address of the maximum available data.	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 stor-
       age areas. Therefore, only programs with growing data areas should need to use sbrk().

       The current value of the program break is reliably returned by ``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() func-
       tion.

       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 pro-
       grams 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 may be set to the following value: Indicates an attempt
       to set a break value to less than the initial value at program startup.	The requested change would allocate more space than allowed by the
       limit as returned by the getrlimit() function.

RELATED INFORMATION

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

       Standards: standards(5) delim off

																	    brk(2)

brk(2)								   System Calls 							    brk(2)

NAME

       brk, sbrk - change the amount of space allocated for the calling process's data segment

SYNOPSIS

       #include <unistd.h>

       int brk(void *endds);

       void *sbrk(intptr_t incr);

DESCRIPTION

       The  brk()  and	sbrk()	functions are used to change dynamically the amount of space allocated for the calling process's data segment (see
       exec(2)). The change is made by resetting the process's break value and allocating the appropriate amount of space. The break value is  the
       address	of  the  first	location beyond the end of the data segment. The amount of allocated space increases as the break value increases.
       Newly allocated space is set to zero. If, however, the same memory space  is reallocated to the same process its contents are undefined.

       When a program begins execution using execve() the break is set at the highest location defined by the program and data storage areas.

       The getrlimit(2) function may be used to determine the maximum permissible size of the data segment; it is not possible to  set	the  break
       beyond the rlim_max value returned from a call to getrlimit(), that is to say, "end + rlim.rlim_max." See end(3C).

       The brk() function sets the break value to endds and changes the allocated space accordingly.

       The sbrk() function adds  incr function bytes to the break value and changes the allocated space accordingly. The incr function can be neg-
       ative, in which case the amount of allocated space is decreased.

RETURN VALUES

       Upon successful completion, brk() returns 0. Otherwise, it returns -1 and sets errno to indicate the error.

       Upon successful completion, sbrk() returns the prior break value.  Otherwise, it returns (void *)-1 and sets errno to indicate the error.

ERRORS

       The brk() and sbrk() functions will fail and no additional memory will be allocated if:

       ENOMEM	 The data segment size limit as set by setrlimit() (see getrlimit(2)) would be exceeded; the maximum possible size of a data  seg-
		 ment  (compiled  into	the system) would be exceeded; insufficient space exists in the swap area to support the expansion; or the
		 new break value would extend into an area of the address space defined by some previously established mapping (see mmap(2)).

       EAGAIN	 Total amount of system memory available for private pages is temporarily insufficient. This  may  occur  even	though	the  space
		 requested was less than the maximum data segment size (see  ulimit(2)).

USAGE

       The  behavior  of  brk()  and  sbrk()  is  unspecified if an application also uses any other memory functions (such as malloc(3C), mmap(2),
       free(3C)). The brk() and sbrk() functions have been used in specialized cases where no other memory allocation function provided  the  same
       capability.   The  use  of mmap(2) is now preferred because it can be used portably with all other memory allocation functions and with any
       function that uses other allocation functions.

       It is unspecified whether the pointer returned by sbrk() is aligned suitably for any purpose.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |MT-Safe			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       exec(2), getrlimit(2), mmap(2), shmop(2), ulimit(2), end(3C), free(3C), malloc(3C)

NOTES

       The value of incr may be adjusted by the system before setting the new break value.  Upon successful completion, the implementation guaran-
       tees a minimum of incr bytes will be added to the data segment if incr is a positive value.  If incr is a negative value, a maximum of incr
       bytes will be removed from the data segment.  This adjustment may not be necessary for all machine architectures.

       The value of the arguments to both brk() and sbrk() are rounded up for alignment with eight-byte boundaries.

BUGS

       Setting the break may fail due to a temporary lack of swap space. It is not possible to distinguish this from a failure caused by exceeding
       the maximum size of the data segment without consulting getrlimit().

SunOS 5.11							    14 Jan 1997 							    brk(2)