FGETC(3)                   POSIX Programmer's Manual                  FGETC(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
       fgetc -- get a byte from a stream

SSYYNNOOPPSSIISS
       #include <stdio.h>

       int fgetc(FILE *_s_t_r_e_a_m);

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.

       If the end-of-file indicator for the input stream pointed to by _s_t_r_e_a_m
       is not set and a next byte is present, the _f_g_e_t_c() function shall
       obtain the next byte as an uunnssiiggnneedd cchhaarr converted to an iinntt, from the
       input stream pointed to by _s_t_r_e_a_m, and advance the associated file
       position indicator for the stream (if defined). Since _f_g_e_t_c() operates
       on bytes, reading a character consisting of multiple bytes (or ``a
       multi-byte character'') may require multiple calls to _f_g_e_t_c().

       The _f_g_e_t_c() function may mark the last data access timestamp of the
       file associated with _s_t_r_e_a_m for update. The last data access timestamp
       shall be marked for update by the first successful execution of
       _f_g_e_t_c(), _f_g_e_t_s(), _f_r_e_a_d(), _f_s_c_a_n_f(), _g_e_t_c(), _g_e_t_c_h_a_r(), _g_e_t_d_e_l_i_m(),
       _g_e_t_l_i_n_e(), _g_e_t_s(), or _s_c_a_n_f() using _s_t_r_e_a_m that returns data not
       supplied by a prior call to _u_n_g_e_t_c().

RREETTUURRNN VVAALLUUEE
       Upon successful completion, _f_g_e_t_c() shall return the next byte from the
       input stream pointed to by _s_t_r_e_a_m.  If the end-of-file indicator for
       the stream is set, or if the stream is at end-of-file, the end-of-file
       indicator for the stream shall be set and _f_g_e_t_c() shall return EOF. If
       a read error occurs, the error indicator for the stream shall be set,
       _f_g_e_t_c() shall return EOF, and shall set _e_r_r_n_o to indicate the error.

EERRRROORRSS
       The _f_g_e_t_c() function shall fail if data needs to be read and:

       EEAAGGAAIINN The O_NONBLOCK flag is set for the file descriptor underlying
              _s_t_r_e_a_m and the thread would be delayed in the _f_g_e_t_c() operation.

       EEBBAADDFF  The file descriptor underlying _s_t_r_e_a_m is not a valid file
              descriptor open for reading.

       EEIINNTTRR  The read operation was terminated due to the receipt of a
              signal, and no data was transferred.

       EEIIOO    A physical I/O error has occurred, or the process is in a
              background process group attempting to read from its controlling
              terminal, and either the calling thread is blocking SIGTTIN or
              the process is ignoring SIGTTIN or the process group of the
              process is orphaned.  This error may also be generated for
              implementation-defined reasons.

       EEOOVVEERRFFLLOOWW
              The file is a regular file and an attempt was made to read at or
              beyond the offset maximum associated with the corresponding
              stream.

       The _f_g_e_t_c() function may fail if:

       EENNOOMMEEMM Insufficient storage space is available.

       EENNXXIIOO  A request was made of a nonexistent device, or the request was
              outside the capabilities of the device.

       _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
       If the integer value returned by _f_g_e_t_c() is stored into a variable of
       type cchhaarr and then compared against the integer constant EOF, the
       comparison may never succeed, because sign-extension of a variable of
       type cchhaarr on widening to integer is implementation-defined.

       The _f_e_r_r_o_r() or _f_e_o_f() functions must be used to distinguish between an
       error condition and an end-of-file condition.

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_e_o_f(), _f_e_r_r_o_r(), _f_g_e_t_s(), _f_r_e_a_d(),
       _f_s_c_a_n_f(), _g_e_t_c_h_a_r(), _g_e_t_c(), _g_e_t_s(), _u_n_g_e_t_c()

       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                             FGETC(3)
