The fputc() function shall write the byte specified by c
(converted to an unsigned char) to the output
stream pointed to by stream, at the position indicated by the
associated file-position indicator for the stream (if
defined), and shall advance the indicator appropriately. If the file
cannot support positioning requests, or if the stream was
opened with append mode, the byte shall be appended to the output
st_ctime and st_mtime fields of the file shall be marked
for update between the successful execution of
fputc() and the next successful completion of a call to fflush()
or fclose() on the same stream or a call to exit()
Upon successful completion, fputc() shall return the value it
has written. Otherwise, it shall return EOF, the error
indicator for the stream shall be set, and errno shall be
set to indicate the error.
The fputc() function shall fail if either the stream is
unbuffered or the stream's buffer needs to be
The O_NONBLOCK flag is set for the file descriptor underlying stream
and the process would be delayed in the write
The file descriptor underlying stream is not a valid file descriptor
open for writing.
attempt was made to write to a file that exceeds the maximum file
An attempt was made to write to a file that exceeds the process' file
The file is a regular file and an attempt was made to write at or
beyond the offset maximum.
The write operation was terminated due to the receipt of a signal,
and no data was transferred.
physical I/O error has occurred, or the process is a member of a background
process group attempting to write to its controlling
terminal, TOSTOP is set, the process is neither ignoring nor blocking
SIGTTOU, and the process group of the process is orphaned.
This error may also be returned under implementation-defined conditions.
There was no free space remaining on the device containing the file.
attempt is made to write to a pipe or FIFO that is not open for reading
by any process. A SIGPIPE signal shall also be sent to the
The fputc() function may fail if:
Insufficient storage space is available.
request was made of a nonexistent device, or the request was outside
the capabilities of the device.
The following sections are informative.
ferror() , fopen() , getrlimit() , putc()
, puts() , setbuf() , ulimit() , the Base Definitions
IEEE Std 1003.1-2001, <stdio.h>
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