FGETC(3P) POSIX Programmer's Manual FGETC(3P)
PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the correspond-
ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.
NAME
fgetc -- get a byte from a stream
SYNOPSIS
#include <stdio.h>
int fgetc(FILE *stream);
DESCRIPTION
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.1-2008 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(), get-
line(), gets(), or scanf() using stream that returns data not supplied by a prior call to ungetc().
RETURN VALUE
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.
ERRORS
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.
EXAMPLES
None.
APPLICATION USAGE
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.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
Section 2.5, Standard I/O Streams, feof(), ferror(), fgets(), fread(), fscanf(), getchar(), getc(), gets(), ungetc()
The Base Definitions volume of POSIX.1-2008, <stdio.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technol-
ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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 Stan-
dard is the referee document. The original Standard can be obtained online at http://www.unix.org/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 2013 FGETC(3P)