SETVBUF(3)                 POSIX Programmer's Manual                SETVBUF(3)



PPRROOLLOOGG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

NNAAMMEE
       setvbuf -- assign buffering to a stream

SSYYNNOOPPSSIISS
       #include <stdio.h>

       int setvbuf(FILE *restrict _s_t_r_e_a_m, char *restrict _b_u_f, int _t_y_p_e,
           size_t _s_i_z_e);

DDEESSCCRRIIPPTTIIOONN
       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.

       The _s_e_t_v_b_u_f() function may be used after the stream pointed to by
       _s_t_r_e_a_m is associated with an open file but before any other operation
       (other than an unsuccessful call to _s_e_t_v_b_u_f()) is performed on the
       stream. The argument _t_y_p_e determines how _s_t_r_e_a_m shall be buffered, as
       follows:

        *  {_IOFBF} shall cause input/output to be fully buffered.

        *  {_IOLBF} shall cause input/output to be line buffered.

        *  {_IONBF} shall cause input/output to be unbuffered.

       If _b_u_f is not a null pointer, the array it points to may be used
       instead of a buffer allocated by _s_e_t_v_b_u_f() and the argument _s_i_z_e
       specifies the size of the array; otherwise, _s_i_z_e may determine the size
       of a buffer allocated by the _s_e_t_v_b_u_f() function. The contents of the
       array at any time are unspecified.

       For information about streams, see _S_e_c_t_i_o_n _2_._5, _S_t_a_n_d_a_r_d _I_/_O _S_t_r_e_a_m_s.

RREETTUURRNN VVAALLUUEE
       Upon successful completion, _s_e_t_v_b_u_f() shall return 0. Otherwise, it
       shall return a non-zero value if an invalid value is given for _t_y_p_e or
       if the request cannot be honored, and may set _e_r_r_n_o to indicate the
       error.

EERRRROORRSS
       The _s_e_t_v_b_u_f() function may fail if:

       EEBBAADDFF  The file descriptor underlying _s_t_r_e_a_m is not valid.

       _T_h_e _f_o_l_l_o_w_i_n_g _s_e_c_t_i_o_n_s _a_r_e _i_n_f_o_r_m_a_t_i_v_e_.

EEXXAAMMPPLLEESS
       None.

AAPPPPLLIICCAATTIIOONN UUSSAAGGEE
       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 _s_e_t_v_b_u_f(), allocating a buffer of _s_i_z_e bytes does not necessarily
       imply that all of _s_i_z_e bytes are used for the buffer area.

       Applications should note that many implementations only provide line
       buffering on input from terminal devices.

RRAATTIIOONNAALLEE
       None.

FFUUTTUURREE DDIIRREECCTTIIOONNSS
       None.

SSEEEE AALLSSOO
       _S_e_c_t_i_o_n _2_._5, _S_t_a_n_d_a_r_d _I_/_O _S_t_r_e_a_m_s, _f_o_p_e_n(), _s_e_t_b_u_f()

       The Base Definitions volume of POSIX.1-2017, <<ssttddiioo..hh>>

CCOOPPYYRRIIGGHHTT
       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 .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                           SETVBUF(3)
