Section: POSIX Programmer's Manual (3P)
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.
--- get a byte from a stream
int fgetc(FILE *stream);
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
is not set and a next byte is present, the
function shall obtain the next byte as an
converted to an
from the input stream pointed to by
and advance the associated file position indicator for the stream (if
operates on bytes, reading a character consisting of multiple bytes (or
``a multi-byte character'') may require multiple calls to
function may mark the last data access timestamp of the file
for update. The last data access timestamp shall be marked for
update by the first successful execution of
that returns data not supplied by a prior call to
Upon successful completion,
shall return the next byte from the input stream pointed to by
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
shall return EOF. If a read error occurs, the error indicator for the
stream shall be set,
shall return EOF,
and shall set
to indicate the error.
function shall fail if data needs to be read and:
The O_NONBLOCK flag is set for the file descriptor underlying
and the thread would be delayed in the
The file descriptor underlying
is not a valid file descriptor open for reading.
The read operation was terminated due to the receipt of a signal, and
no data was transferred.
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.
The file is a regular file and an attempt was made to read at or beyond
the offset maximum associated with the corresponding stream.
function may fail if:
Insufficient storage space is available.
A request was made of a nonexistent device, or the request was outside
the capabilities of the device.
The following sections are informative.
If the integer value returned by
is stored into a variable of type
and then compared against the integer constant EOF, the comparison may
never succeed, because sign-extension of a variable of type
on widening to integer is implementation-defined.
functions must be used to distinguish between an error condition and an
, Standard I/O Streams,
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
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