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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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FGETC(3P) POSIX Programmer's Manual FGETC(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.
fgetc — get a byte from a stream
#include <stdio.h>
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
stream is not set and a next byte is present, the fgetc() function
shall obtain the next byte as an unsigned char converted to an
int, from the input stream pointed to by stream, and advance the
associated file position indicator for the stream (if defined).
Since fgetc() operates on bytes, reading a character consisting of
multiple bytes (or ``a multi-byte character'') may require
multiple calls to fgetc().
The fgetc() function may mark the last data access timestamp of
the file associated with stream for update. The last data access
timestamp shall be marked for update by the first successful
execution of fgetc(), fgets(), fread(), fscanf(), getc(),
getchar(), getdelim(), getline(), gets(), or scanf() using stream
that returns data not supplied by a prior call to ungetc().
Upon successful completion, fgetc() shall return the next byte
from the input stream pointed to by stream. 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
fgetc() shall return EOF. If a read error occurs, the error
indicator for the stream shall be set, fgetc() shall return EOF,
and shall set errno to indicate the error.
The fgetc() function shall fail if data needs to be read and:
EAGAIN The O_NONBLOCK flag is set for the file descriptor
underlying stream and the thread would be delayed in the
fgetc() operation.
EBADF The file descriptor underlying stream is not a valid file
descriptor open for reading.
EINTR The read operation was terminated due to the receipt of a
signal, and no data was transferred.
EIO 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.
EOVERFLOW
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 fgetc() function may fail if:
ENOMEM Insufficient storage space is available.
ENXIO A request was made of a nonexistent device, or the request
was outside the capabilities of the device.
The following sections are informative.
None.
If the integer value returned by fgetc() is stored into a variable
of type char and then compared against the integer constant EOF,
the comparison may never succeed, because sign-extension of a
variable of type char on widening to integer is implementation-
defined.
The ferror() or feof() functions must be used to distinguish
between an error condition and an end-of-file condition.
None.
None.
Section 2.5, Standard I/O Streams, feof(3p), ferror(3p),
fgets(3p), fread(3p), fscanf(3p), getchar(3p), getc(3p), gets(3p),
ungetc(3p)
The Base Definitions volume of POSIX.1‐2017, stdio.h(0p)
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(3P)
Pages that refer to this page: stdio.h(0p), fgets(3p), fread(3p), fscanf(3p), getc(3p), getchar(3p), getdelim(3p), gets(3p)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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