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)