изменить размер сегмента данных (change data segment size)
Имя (Name)
brk, sbrk - change data segment size
Синопсис (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 2.19:
_DEFAULT_SOURCE
|| ((_XOPEN_SOURCE >= 500) &&
! (_POSIX_C_SOURCE >= 200112L))
From glibc 2.12 to 2.19:
_BSD_SOURCE || _SVID_SOURCE
|| ((_XOPEN_SOURCE >= 500) &&
! (_POSIX_C_SOURCE >= 200112L))
Before glibc 2.12:
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500
Описание (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 location of the program break.
Возвращаемое значение (Return value)
On success, brk() returns zero. On error, -1 is returned, and
errno is set to ENOMEM.
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.
Стандарты (Conforming to)
4.3BSD; SUSv1, marked LEGACY in SUSv2, removed in POSIX.1-2001.
Примечание (Note)
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.
C library/kernel differences
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.
Смотри также (See also)
execve(2), getrlimit(2), end(3), malloc(3)
