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UNGETC(3) Library Functions Manual UNGETC(3)

ungetcun-get character from input stream

#include <stdio.h>

ungetc(int c, FILE *stream);

The () function pushes the character c (converted to an unsigned char) back onto the input stream pointed to by stream. The pushed-backed characters will be returned by subsequent reads on the stream (in reverse order). A successful intervening call, using the same stream, to one of the file positioning functions (fseek(3), fsetpos(3), or rewind(3)) will discard the pushed back characters.

One character of push-back is guaranteed, but as long as there is sufficient memory, an effectively infinite amount of pushback is allowed.

If a character is successfully pushed-back, the end-of-file indicator for the stream is cleared.

The ungetc() function returns the character pushed-back after the conversion, or EOF if the operation fails. If the value of the argument c character equals EOF, the operation will fail and the stream will remain unchanged.

fseek(3), getc(3), setvbuf(3), ungetwc(3)

The ungetc() function conforms to ANSI X3.159-1989 (“ANSI C89”).

The ungetc() function first appeared in Version 7 AT&T UNIX.

December 1, 2017 OpenBSD-6.8