brk man page on Ultrix

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brk(2)									brk(2)

Name
       brk, sbrk - change core allocation

Syntax
       #include <sys/types.h>

       caddr_t brk(addr)
       caddr_t addr;

       caddr_t sbrk(incr)
       int incr;

Description
       The system call sets the system's idea of the lowest data segment loca‐
       tion not used by the program (called the break) to addr (rounded up  to
       the  next  multiple of the system's page size).	Locations greater than
       addr and below the stack pointer are not in the address space and  will
       thus cause a memory violation if accessed.

       In  the	alternate  function 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 using the break is set at  the  highest
       location	 defined  by  the program and data storage areas.  Ordinarily,
       therefore, only programs with growing data areas need to use

       The system call may be used to determine the maximum  permissible  size
       of  the	data segment.  It will not be possible to set the break beyond
       the rlim_max value returned from a call to for  example,	 etext	+  rlp
       -rlim_max.  See for the definition of etext.

Return Values
       If  the call is successful, returns a 0 value.  If the program requests
       more memory than the system limit, returns -1.  If the break could  not
       be set, returns -1.

Restrictions
       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

Diagnostics
       The  call fails and no additional memory is allocated under the follow‐
       ing conditions:

       [ENOMEM]	      The limit, as set by is exceeded.

       [ENOMEM]	      The maximum possible size of a  data  segment  (compiled
		      into the system) is exceeded.

       [ENOMEM]	      Insufficient  space  exists  in the swap area to support
		      the expansion.

See Also
       execve(2), getrlimit(2), setrlimit(2), end(3), malloc(3)

				      VAX				brk(2)
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