This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the corresponding Linux
manual page for details of Linux behavior), or the interface may not be
implemented on Linux.
setbuf — assign buffering to a stream
void setbuf(FILE *restrict stream, char *restrict buf);
The functionality described on this reference page is aligned with the
ISO C standard. Any conflict between the requirements described here
and the ISO C standard is unintentional. This volume of
POSIX.1‐2017 defers to the ISO C standard.
Except that it returns no value, the function call:
shall be equivalent to:
setvbuf(stream, buf, _IOFBF, BUFSIZ)
if buf is not a null pointer, or to:
setvbuf(stream, buf, _IONBF, BUFSIZ)
if buf is a null pointer.
The setbuf() function shall not return a value.
Although the setvbuf() interface may set errno in defined ways,
the value of errno after a call to setbuf() is unspecified.
The following sections are informative.
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.
With setbuf(), allocating a buffer of BUFSIZ bytes does not
necessarily imply that all of BUFSIZ bytes are used for the buffer area.
Since errno is not required to be unchanged on success, in
order to correctly detect and possibly recover from errors, applications
should use setvbuf() instead of setbuf().
Section 2.5, Standard I/O Streams, fopen(),
The Base Definitions volume of POSIX.1‐2017,
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1-2017, Standard for Information Technology -- Portable Operating
System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018
Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html .
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