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 unsignedchar 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
The fgetc() function may mark the st_atime field of the file
associated with stream for update. The st_atime field shall be
marked for update by the first successful execution of fgetc(),
fgets(), fgetwc(), fgetws(), fread(),
fscanf(), getc(), getchar(), gets(), or
scanf() using stream that returns data not supplied by a prior
call to ungetc() or ungetwc().
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:
The O_NONBLOCK flag is set for the file descriptor
underlying stream and the process would be delayed in the
The file descriptor underlying stream 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 process is ignoring or blocking the SIGTTIN signal or the
process group is orphaned. This error may also be generated for
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:
Insufficient storage space is available.
A request was made of a nonexistent device, or the request
was outside the capabilities of the device.
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.
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 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