libc.info: putc

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`putc'--write a character (macro)

*Synopsis*
     #include <stdio.h>
     int putc(int CH, FILE *FP);
   *Description*
`putc' is a macro, defined in `stdio.h'.  `putc' writes the argument CH
to the file or stream identified by FP, after converting it from an
`int' to an `unsigned char'.
   If the file was opened with append mode (or if the stream cannot
support positioning), then the new character goes at the end of the
file or stream.  Otherwise, the new character is written at the current
value of the position indicator, and the position indicator advances by
one.
   For a subroutine version of this macro, see `fputc'.
*Returns*
If successful, `putc' returns its argument CH.  If an error intervenes,
the result is `EOF'.  You can use ``ferror(FP)'' to query for errors.
*Portability*
ANSI C requires `putc'; it suggests, but does not require, that `putc'
be implemented as a macro.  The standard explicitly permits macro
implementations of `putc' to use the FP argument more than once;
therefore, in a portable program, you should not use an expression with
side effects as this argument.
   Supporting OS subroutines required: `close', `fstat', `isatty',
`lseek', `read', `sbrk', `write'.