UNGETC(3C) Standard C Library Functions UNGETC(3C)
NAME
ungetc - push byte back into input stream
SYNOPSIS
#include <stdio.h>
int ungetc(
int c,
FILE *stream);
DESCRIPTION
The
ungetc() function pushes the byte specified by
c (converted to an
unsigned char) back onto the input stream pointed to by
stream. The
pushed-back bytes will 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(3C),
fsetpos(3C) or
rewind(3C)) discards any pushed-back
bytes for the stream. The external storage corresponding to the
stream is unchanged.
Four bytes of push-back are guaranteed. 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 fails
and the input stream is unchanged.
A successful call to
ungetc() clears 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 will 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 indeterminate after the call.
RETURN VALUES
Upon successful completion,
ungetc() returns the byte pushed back
after conversion. Otherwise it returns
EOF.ERRORS
No errors are defined.
ATTRIBUTES
See
attributes(7) for descriptions of the following attributes:
+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Standard |
+--------------------+-----------------+
|MT-Level | MT-Safe |
+--------------------+-----------------+
SEE ALSO
read(2),
Intro(3),
__fsetlocking(3C),
fseek(3C),
fsetpos(3C),
getc(3C),
setbuf(3C),
stdio(3C),
attributes(7),
standards(7) September 10, 2003 UNGETC(3C)
