ungetwc(3C) Standard C Library Functions ungetwc(3C)NAME
ungetwc - push wide-character code back into input stream
SYNOPSIS
#include <stdio.h>
#include <wchar.h>
wint_t ungetwc(wint_t wc, FILE *stream);
DESCRIPTION
The ungetwc() function pushes the character corresponding to the wide character code specified by wc back onto the input stream pointed to
by stream. The pushed-back characters will be returned by subsequent reads on that stream in the reverse order of their pushing. A success-
ful 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 characters for the stream. The external storage corresponding to the stream is unchanged.
One character of push-back is guaranteed. If ungetwc() 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 wc equals that of the macro WEOF, the operation fails and the input stream is unchanged.
A successful call to ungetwc() 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 characters will be the same as it was before the characters were pushed back. The file-position
indicator is decremented (by one or more) by each successful call to ungetwc(); if its value was 0 before a call, its value is indetermi-
nate after the call.
RETURN VALUES
Upon successful completion, ungetwc() returns the wide-character code corresponding to the pushed-back character. Otherwise it returns
WEOF.
ERRORS
The ungetwc() function may fail if:
EILSEQ An invalid character sequence is detected, or a wide-character code does not correspond to a valid character.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
|ATTRIBUTE TYPE |ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Interface Stability |Standard |
+-----------------------------+-----------------------------+
|MT-Level |MT-Safe |
+-----------------------------+-----------------------------+
SEE ALSO read(2), fseek(3C), fsetpos(3C), rewind(3C), setbuf(3C), attributes(5), standards(5)SunOS 5.11 14 Aug 2002 ungetwc(3C)
Check Out this Related Man Page
ungetc(3) Library Functions Manual ungetc(3)NAME
ungetc, ungetwc - Pushes a byte or wide-character code back into the input stream
LIBRARY
Standard C Library (libc.so, libc.a)
SYNOPSIS
#include <stdio.h>
int ungetc(
int c,
FILE *stream);
#include <wchar.h>
wint_t ungetwc(
wint_t wchar,
FILE *stream);
For the ungetwc() function, application developers may want to specify an #include statement for <stdio.h> before the one for <wchar.h> if
programs are being developed for multiple platforms. The additional #include statement is not required on Tru64 UNIX systems or by ISO or
X/Open standards, but may be required on other vendors' systems that conform to these standards.
STANDARDS
Interfaces documented on this reference page conform to industry standards as follows:
ungetc(), ungetwc(): ISO C, XPG4, XPG4-UNIX
Refer to the standards(5) reference page for more information about industry standards and associated tags.
PARAMETERS
Specifies a byte to be inserted into the input stream. Specifies the input stream. Specifies a wide-character code.
DESCRIPTION
The ungetc() function converts the byte specified by the c parameter into an unsigned char and inserts it into the buffer associated with
the input stream specified by the stream parameter. This causes the next call to the getc() function to return c.
If the c parameter has a value equal to EOF, the ungetc() function does not place anything in the buffer and the input stream is unchanged.
The ungetwc() function inserts the wide character specified by wchar into the buffer associated with the input stream. The wide character
may consist of one or more bytes. This causes the next call to the getwc() function to return the value of the wchar parameter.
If the ungetwc() wchar parameter is WEOF, the ungetwc() function does not place anything in the buffer and the input stream is unchanged.
A call to one of the file-positioning functions (fseek(), fsetpos(), or rewind()), if it uses the same stream and intervenes between a call
to ungetc() or ungetwc() and getc() or getwc(), discards any pushed back bytes for the stream. The value of the file-position indicator
after reading or discarding pushed-back bytes will be the same as it was before the bytes were pushed back.
A successful call to ungetc() or ungetwc() clears the end-of-file indicator and decrements the file-position indicator for the stream. If
the value of the file-position indicator is zero before the call, the value is indeterminate after the call. These functions do not have
any effect on the external storage corresponding to the stream.
One character of push back is guaranteed (this corresponds to one byte for ungetc()) and one or more bytes for ungetwc()); however, if one
of these functions is called too many times on the same stream without an intervening read or file-positioning operation on that stream,
industry standards specify that the functions may fail. (Applications do not encounter this failure on Tru64 UNIX systems. However, results
are unpredictable if applications intermix calls to ungetc() and ungetwc() on the same stream.)
RETURN VALUES
On successful insertion of the converted byte into the stream, the ungetc() function returns the value of c. Otherwise, the function
returns EOF.
On successful insertion of the converted wide character into the stream, the ungetwc() function returns the value of wchar. Otherwise, the
function returns WEOF.
ERRORS
If the following condition occurs, the ungetwc() function sets errno to the corresponding value: An invalid byte sequence is detected, or a
wide-character code does not correspond to a valid single-byte or multibyte character in the current locale.
RELATED INFORMATION
Functions: fseek(3), getc(3), getwc(3), setbuf(3)
Standards: standards(5) delim off
ungetc(3)