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### 4.20 `fputc`—write a character on a stream or file

Synopsis

         #include <stdio.h>
         int fputc(int ch, FILE *fp);

         #include <stdio.h>
         int _fputc_r(struct _rent *ptr, int ch, FILE *fp);

Description
`fputc` converts the argument ch from an `int` to an `unsigned char`, then writes it to the file or stream identified by fp.

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 oadvances by one.

For a macro version of this function, see `putc`.

The `_fputc_r` function is simply a reentrant version of `fputc` that takes an additional reentrant structure argument: ptr.

Returns
If successful, `fputc` returns its argument ch. If an error intervenes, the result is `EOF`. You can use ``ferror(`fp`)`' to query for errors.

Portability
`fputc` is required by ANSI C.

Supporting OS subroutines required: `close`, `fstat`, `isatty`, `lseek`, `read`, `sbrk`, `write`.