setbuf, setvbuf, setvbuf_unlocked, setbuffer, setlinebuf -
Assign buffering to a stream
char *buffer ); int setvbuf(
size_t size ); int setvbuf_unlocked(
size_t size ); void setbuffer(
int size ); void setlinebuf(
FILE *stream );
Standard C Library (libc)
Interfaces documented on this reference page conform to
industry standards as follows:
setbuf(), setvbuf(): XPG4, XPG4-UNIX
Refer to the standards(5) reference page for more information
about industry standards and associated tags.
Specifies the input/output stream. Points to a character
array. Determines how the stream parameter is buffered.
Specifies the size of the buffer to be used.
The setbuf() function causes the character array pointed
to by the buffer parameter to be used instead of an automatically
allocated buffer. Use the setbuf() function
after a stream has been opened but before it is read or
If the buffer parameter is a null pointer, input/output is
A constant, BUFSIZ, defined in the stdio.h header file,
tells how large an array is needed:
For the setvbuf() function, the mode parameter determines
how the stream parameter is buffered: Causes input/output
to be fully buffered. Causes output to be line buffered.
The buffer is flushed when a new line is written, the
buffer is full, or input is requested. Causes input/output
to be completely unbuffered.
If the buffer parameter is not a null pointer, the array
that the parameter points to is used for buffering instead
of a buffer that is automatically allocated. The size
parameter specifies the size of the buffer to be used. The
constant BUFSIZ in the stdio.h header file is one buffer
size. If input/output is unbuffered, the buffer and size
parameters are ignored. The setbuffer() function, an
alternate form of the setbuf() function, is used after
stream has been opened but before it is read or written.
The character array buffer, whose size is determined by
the size parameter, is used instead of an automatically
allocated buffer. If the buffer parameter is a null
pointer, input/output is completely unbuffered.
The setbuffer() function is not needed under normal circumstances,
since the default file I/O buffer size is
The setlinebuf() function is used to change stdout or
stderr from block buffered or unbuffered to line buffered.
Unlike the setbuf() and setbuffer() functions, the setlinebuf()
function can be used any time the file descriptor
A buffer is normally obtained from the malloc() function
at the time of the first getc() or putc() function on the
file, except that the standard error stream, stderr, is
normally not buffered.
Output streams directed to terminals are always either
line buffered or unbuffered.
The setvbuf_unlocked() function is functionally identical
to the setvbuf() function, except that setvbuf_unlocked()
may be safely used only within a scope that is protected
by the flockfile() and funlockfile() functions used as a
pair. The caller must ensure that the stream is locked
before these functions are used.
A common source of error is allocating buffer space as an
automatic variable in a code block, and then failing to
close the stream in the same block.
The setvbuf() and setvbuf_unlocked() functions return zero
when successful. If they cannot honor the request, or if
you give an invalid value in the mode argument, they
return a nonzero value.
If the following condition occurs, the setvbuf() function
sets errno to the corresponding value. The file descriptor
that underlies stream is invalid.
Functions: fopen(3), fread(3), getc(3), getwc(3), malloc(3), putc(3), putwc(3)
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