UNGETC(3) Library Functions Manual UNGETC(3)

NAME

ungetc — push byte back into input stream

SYNOPSIS

#include <stdio.h>

int ungetc(int c, FILE *stream);

DESCRIPTION

[CX] The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1-2008 defers to the ISO C standard.

The ungetc () function shall push the byte specified by c (converted to an unsigned char) back onto the input stream pointed to by stream. The pushed-back bytes shall be returned by subsequent reads on that stream in the reverse order of their pushing. A successful intervening call (with the stream pointed to by stream) to a file-positioning function ( fseek(3), [CX] fseeko(3), fsetpos(3), or rewind(3)) [CX] or fflush(3) shall discard any pushed-back bytes for the stream. The external storage corresponding to the stream shall be unchanged.

One byte of push-back shall be provided. If ungetc () is called too many times on the same stream without an intervening read or file-positioning operation on that stream, the operation may fail.

If the value of c equals that of the macro EOF, the operation shall fail and the input stream shall be left unchanged.

A successful call to ungetc () shall clear the end-of-file indicator for the stream. The value of the file-position indicator for the stream after all pushed-back bytes have been read, or discarded by calling fseek(3), [CX] fseeko(3), fsetpos(3), or rewind(3) [CX] (but not fflush(3)), shall be the same as it was before the bytes were pushed back. The file-position indicator is decremented by each successful call to ungetc (); if its value was 0 before a call, its value is unspecified after the call.