Путеводитель по Руководству Linux

  User  |  Syst  |  Libr  |  Device  |  Files  |  Other  |  Admin  |  Head  |



   setbuf    ( 3 )

операции буферизации потока (stream buffering operations)

Имя (Name)

setbuf, setbuffer, setlinebuf, setvbuf - stream buffering
       operations

Синопсис (Synopsis)

#include <stdio.h>

int setvbuf(FILE *restrict stream, char *restrict buf, int mode, size_t size);

void setbuf(FILE *restrict stream, char *restrict buf); void setbuffer(FILE *restrict stream, char *restrict buf, size_t size); void setlinebuf(FILE *stream);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

setbuffer(), setlinebuf(): Since glibc 2.19: _DEFAULT_SOURCE Glibc 2.19 and earlier: _BSD_SOURCE


Описание (Description)

The three types of buffering available are unbuffered, block
       buffered, and line buffered.  When an output stream is
       unbuffered, information appears on the destination file or
       terminal as soon as written; when it is block buffered, many
       characters are saved up and written as a block; when it is line
       buffered, characters are saved up until a newline is output or
       input is read from any stream attached to a terminal device
       (typically stdin).  The function fflush(3) may be used to force
       the block out early.  (See fclose(3).)

Normally all files are block buffered. If a stream refers to a terminal (as stdout normally does), it is line buffered. The standard error stream stderr is always unbuffered by default.

The setvbuf() function may be used on any open stream to change its buffer. The mode argument must be one of the following three macros:

_IONBF unbuffered

_IOLBF line buffered

_IOFBF fully buffered

Except for unbuffered files, the buf argument should point to a buffer at least size bytes long; this buffer will be used instead of the current buffer. If the argument buf is NULL, only the mode is affected; a new buffer will be allocated on the next read or write operation. The setvbuf() function may be used only after opening a stream and before any other operations have been performed on it.

The other three calls are, in effect, simply aliases for calls to setvbuf(). The setbuf() function is exactly equivalent to the call

setvbuf(stream, buf, buf ? _IOFBF : _IONBF, BUFSIZ);

The setbuffer() function is the same, except that the size of the buffer is up to the caller, rather than being determined by the default BUFSIZ. The setlinebuf() function is exactly equivalent to the call:

setvbuf(stream, NULL, _IOLBF, 0);


Возвращаемое значение (Return value)

The function setvbuf() returns 0 on success.  It returns nonzero
       on failure (mode is invalid or the request cannot be honored).
       It may set errno on failure.

The other functions do not return a value.


Атрибуты (Attributes)

For an explanation of the terms used in this section, see
       attributes(7).

┌──────────────────────────────────────┬───────────────┬─────────┐ │Interface Attribute Value │ ├──────────────────────────────────────┼───────────────┼─────────┤ │setbuf(), setbuffer(), setlinebuf(), │ Thread safety │ MT-Safe │ │setvbuf() │ │ │ └──────────────────────────────────────┴───────────────┴─────────┘


Стандарты (Conforming to)

The setbuf() and setvbuf() functions conform to C89 and C99.

Примечание (Note)

POSIX notes that the value of errno is unspecified after a call
       to setbuf() and further notes that, since the value of errno is
       not required to be unchanged after a successful call to setbuf(),
       applications should instead use setvbuf() in order to detect
       errors.

Ошибки (баги) (Bugs)

You must make sure that the space that buf points to still exists
       by the time stream is closed, which also happens at program
       termination.  For example, the following is invalid:

#include <stdio.h>

int main(void) { char buf[BUFSIZ]; setbuf(stdout, buf); printf("Hello, world!\n"); return 0; }


Смотри также (See also)

stdbuf(1), fclose(3), fflush(3), fopen(3), fread(3), malloc(3),
       printf(3), puts(3)