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NAME
ungetc - push byte back into input stream
SYNOPSIS
#include <stdio.h> int ungetc(int c, FILE *stream);
DESCRIPTION
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(), fsetpos(), or rewind()) 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 reading or discarding all pushed-back bytes 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.
RETURN VALUE
Upon successful completion, ungetc() shall return the byte pushed back after conversion. Otherwise, it
shall return EOF.
ERRORS
No errors are defined.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
None.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
fseek() , getc() , fsetpos() , read() , rewind() , setbuf() , the Base Definitions volume of
IEEE Std 1003.1-2001, <stdio.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition,
Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers,
Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The
original Standard can be obtained online at http://www.opengroup.org/unix/online.html .