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PUTC(3) Library Functions Manual PUTC(3)

fputc, putc, putchar, putw
output a character or word to a stream

#include <stdio.h>
int
fputc(int c, FILE *stream);
int
putc(int c, FILE *stream);
int
putchar(int c);
int
putw(int w, FILE *stream);

The fputc() function writes the character c (converted to an unsigned char) to the output stream pointed to by stream.
putc() acts essentially identically to fputc(), but is a macro that expands in-line. It may evaluate stream more than once, so arguments given to putc() should not be expressions with potential side effects.
putchar() is identical to putc() with an output stream of stdout.
The putw() function writes the specified int w to the named output stream.

The functions fputc(), putc(), and putchar() return the character written. If an error occurs, the value EOF is returned and the global variable errno is set to indicate the error. The putw() function returns 0 on success; EOF is returned if a write error occurs, or if an attempt is made to write a read-only stream. The global variable errno may be set to indicate the error.

The function putw() may also fail and set errno for any of the errors specified for the routines write(2) or realloc(3).

ferror(3), fopen(3), getc(3), putwc(3), stdio(3)

The functions fputc(), putc(), and putchar(), conform to ANSI X3.159-1989 (“ANSI C89”).

The putc() and putw() functions first appeared in Version 1 AT&T UNIX; putchar() in Version 2 AT&T UNIX; and fputc() in Version 7 AT&T UNIX.

Since the size and byte order of an int may vary from one machine to another, putw() is not recommended for portable applications.
December 1, 2017 OpenBSD-current