illumos: manual page: putc.3c

FPUTC(3C) Standard C Library Functions FPUTC(3C)

NAME

fputc, putc, putc_unlocked, putchar, putchar_unlocked, putw - put a byte
on a stream

SYNOPSIS

#include <stdio.h>

int fputc(int c, FILE *stream);

int putc(int c, FILE *stream);

int putc_unlocked(int c, FILE *stream);

int putchar(int c);

int putchar_unlocked(int c);

int putw(int w, FILE *stream);

DESCRIPTION

The fputc() function writes 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 advances the indicator appropriately. If the file cannot
support positioning requests, or if the stream was opened with append
mode, the byte is appended to the output stream.

The st_ctime and st_mtime fields of the file will be marked for update
between the successful execution of fputc() and the next successful
completion of a call to fflush(3C) or fclose(3C) on the same stream or a
call to exit(3C) or abort(3C).

The putc() routine behaves like fputc(), except that it is implemented as
a macro. It runs faster than fputc(), but it takes up more space per
invocation and its name cannot be passed as an argument to a function
call.

The call putchar(c) is equivalent to putc(c, stdout). The putchar()
routine is implemented as a macro.

The putc_unlocked() and putchar_unlocked() routines are variants of
putc() and putchar(), respectively, that do not lock the stream. It is
the caller's responsibility to acquire the stream lock before calling
these routines and releasing the lock afterwards; see flockfile(3C) and
stdio(3C). These routines are implemented as macros.

The putw() function writes the word (that is, type int) w to the output
stream (at the position at which the file offset, if defined, is
pointing). The size of a word is the size of a type int and varies from
machine to machine. The putw() function neither assumes nor causes
special alignment in the file.

The st_ctime and st_mtime fields of the file will be marked for update
between the successful execution of putw() and the next successful
completion of a call to fflush(3C) or fclose(3C) on the same stream or a
call to exit(3C) or abort(3C).

RETURN VALUES

Upon successful completion, fputc(), putc(), putc_unlocked(), putchar(),
and putchar_unlocked() return the value that was written. Otherwise,
these functions return EOF, the error indicator for the stream is set,
and errno is set to indicate the error.

Upon successful completion, putw() returns 0. Otherwise, it returns a
non-zero value, sets the error indicator for the associated stream, and
sets errno to indicate the error.

An unsuccessful completion will occur, for example, if the file
associated with stream is not open for writing or if the output file
cannot grow.

ERRORS

The fputc(), putc(), putc_unlocked(), putchar(), putchar_unlocked(), and
putw() functions will fail if either the stream is unbuffered or the
stream's buffer needs to be flushed, and:

EAGAIN
The O_NONBLOCK flag is set for the file descriptor underlying
stream and the process would be delayed in the write operation.

EBADF
The file descriptor underlying stream is not a valid file
descriptor open for writing.

EFBIG
An attempt was made to write to a file that exceeds the maximum
file size or the process' file size limit.

EFBIG
The file is a regular file and an attempt was made to write at
or beyond the offset maximum.

EINTR
The write 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 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. stream was created by open_wmemstream(3C)
and a wide-character or byte sequence buffered is invalid in
the current locale. This error may also be returned under
implementation-dependent conditions.

ENOSPC
There was no free space remaining on the device containing the
file.

EPIPE
An attempt is made to write to a pipe or FIFO that is not open
for reading by any process. A SIGPIPE signal will also be sent
to the calling thread.

The fputc(), putc(), putc_unlocked(), putchar(), putchar_unlocked(), and
putw() functions may fail if:

ENOMEM
Insufficient storage space is available.

ENXIO
A request was made of a non-existent device, or the request was
outside the capabilities of the device.

USAGE

Functions exist for the putc(), putc_unlocked(), putchar(), and
putchar_unlocked() macros. To get the function form, the macro name must
be undefined (for example, #undef putc).

When the macro forms are used, putc() and putc_unlocked() evaluate the
stream argument more than once. In particular, putc(c, *f++); does not
work sensibly. The fputc() function should be used instead when
evaluating the stream argument has side effects.

Because of possible differences in word length and byte ordering, files
written using putw() are implementation-dependent, and possibly cannot be
read using getw(3C) by a different application or by the same application
running in a different environment.

The putw() function is inherently byte stream oriented and is not tenable
in the context of either multibyte character streams or wide-character
streams. Application programmers are encouraged to use one of the
character-based output functions instead.

ATTRIBUTES

NOTES

The fputc(), putc(), putchar(), and putw() routines are MT-Safe in
multithreaded applications. The putc_unlocked() and putchar_unlocked()
routines are unsafe in multithreaded applications.

March 25, 2020 FPUTC(3C)