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man pages section 3: Basic Library Functions

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Updated: Wednesday, July 27, 2022



ungetwc - push wide-character code back into input stream


#include <stdio.h>
#include <wchar.h>

wint_t ungetwc(wint_t wc, FILE *stream);


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 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 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 indeterminate after the call.

Return Values

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


The ungetwc() function may fail if:


An invalid character sequence is detected, or a wide-character code does not correspond to a valid character.


See attributes(7) for descriptions of the following attributes:

Interface Stability

See Also

setbuf(3C), read(2), fseek(3C), fsetpos(3C), rewind(3C), attributes(7), standards(7)