The Open Group Base Specifications Issue 7
IEEE Std 1003.1-2008, 2016 Edition
Copyright © 2001-2016 The IEEE and The Open Group

#### NAME

> ungetwc - push wide-character code back into the input stream

#### SYNOPSIS

> ``#include <stdio.h>
> #include <wchar.h>
> wint_t ungetwc(wint_t` wc`, 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 ungetwc() function shall push the character corresponding to the wide-character code specified by wc back onto the input stream pointed to by stream. The pushed-back characters 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(), [CX] fseeko(), fsetpos(), or rewind()) [CX] or fflush() shall discard any pushed-back characters for the stream. The external storage corresponding to the stream is unchanged.

> At least one character of push-back shall be provided. 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 shall fail and the input stream shall be left unchanged.

> A successful call to ungetwc() shall clear the end-of-file indicator for the stream. The value of the file-position indicator for the stream after all pushed-back characters have been read, or discarded by calling fseek(), [CX] fseeko(), fsetpos(), or rewind() [CX] (but not fflush()), shall 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 unspecified after the call.

#### RETURN VALUE

> Upon successful completion, ungetwc() shall return the wide-character code corresponding to the pushed-back character. Otherwise, it shall return WEOF.

#### ERRORS

> The ungetwc() function may fail if:

> [EILSEQ]
>   [CX] An invalid character sequence is detected, or a wide-character code does not correspond to a valid character.

The following sections are informative.

#### EXAMPLES

> None.

#### APPLICATION USAGE

> None.

#### RATIONALE

> None.

#### FUTURE DIRECTIONS

> None.

#### SEE ALSO

> Standard I/O Streams, fseek, fsetpos, read, rewind, setbuf

> XBD <stdio.h>, <wchar.h>

#### CHANGE HISTORY

> First released in Issue 4. Derived from the MSE working draft.

#### Issue 5

> The Optional Header (OH) marking is removed from <stdio.h>.

#### Issue 6

> The [EILSEQ] optional error condition is marked CX.

#### Issue 7

> POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0690 [87,93], XSH/TC1-2008/0691 [87], and XSH/TC1-2008/0692 [14] are applied.

End of informative text.

return to top of page

UNIX ® is a registered Trademark of The Open Group.
POSIX ® is a registered Trademark of The IEEE.
Copyright © 2001-2016 The IEEE and The Open Group, All Rights Reserved
[ Main Index | XBD | XSH | XCU | XRAT ]