The Open Group Base Specifications Issue 7, 2018 edition
IEEE Std 1003.1-2017 (Revision of IEEE Std 1003.1-2008)
Copyright © 2001-2018 IEEE and The Open Group


fgetwc - get a wide-character code from a stream


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

wint_t fgetwc(FILE *


[CX] [Option Start] 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.1-2017 defers to the ISO C standard. [Option End]

The fgetwc() function shall obtain the next character (if present) from the input stream pointed to by stream, convert that to the corresponding wide-character code, and advance the associated file position indicator for the stream (if defined).

If an error occurs, the resulting value of the file position indicator for the stream is unspecified.

[CX] [Option Start] The fgetwc() function may mark the last data access timestamp of the file associated with stream for update. The last data access timestamp shall be marked for update by the first successful execution of fgetwc(), fgetws(), fwscanf(), getwc(), getwchar(), vfwscanf(), vwscanf(), or wscanf() using stream that returns data not supplied by a prior call to ungetwc(). [Option End]

The fgetwc() function shall not change the setting of errno if successful.


Upon successful completion, the fgetwc() function shall return the wide-character code of the character read from the input stream pointed to by stream converted to a type wint_t. If the end-of-file indicator for the stream is set, or if the stream is at end-of-file, the end-of-file indicator for the stream shall be set and fgetwc() shall return WEOF. If a read error occurs, the error indicator for the stream shall be set, fgetwc() shall return WEOF, [CX] [Option Start]  and shall set errno to indicate the error. [Option End] If an encoding error occurs, the error indicator for the stream shall be set, fgetwc() shall return WEOF, and shall set errno to indicate the error.


The fgetwc() function shall fail if data needs to be read and:

[CX] [Option Start] The O_NONBLOCK flag is set for the file descriptor underlying stream and the thread would be delayed in the fgetwc() operation. [Option End]
[CX] [Option Start] The file descriptor underlying stream is not a valid file descriptor open for reading. [Option End]
The data obtained from the input stream does not form a valid character.
[CX] [Option Start] The read operation was terminated due to the receipt of a signal, and no data was transferred. [Option End]
[CX] [Option Start] A physical I/O error has occurred, or the process is in a background process group attempting to read from its controlling terminal, and either the calling thread is blocking SIGTTIN or the process is ignoring SIGTTIN or the process group of the process is orphaned. This error may also be generated for implementation-defined reasons. [Option End]
[CX] [Option Start] The file is a regular file and an attempt was made to read at or beyond the offset maximum associated with the corresponding stream. [Option End]

The fgetwc() function may fail if:

[CX] [Option Start] Insufficient storage space is available. [Option End]
[CX] [Option Start] A request was made of a nonexistent device, or the request was outside the capabilities of the device. [Option End]

The following sections are informative.




The ferror() or feof() functions must be used to distinguish between an error condition and an end-of-file condition.






Standard I/O Streams, feof, ferror, fopen

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


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

Issue 5

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

Large File Summit extensions are added.

Issue 6

Extensions beyond the ISO C standard are marked.

The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:

IEEE Std 1003.1-2001/Cor 2-2004, item XSH/TC2/D6/33 is applied, updating the [EAGAIN] error in the ERRORS section from ``the process would be delayed'' to ``the thread would be delayed''.

Issue 7

Austin Group Interpretation 1003.1-2001 #051 is applied, clarifying the RETURN VALUE section.

Changes are made related to support for finegrained timestamps.

POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0136 [105], XSH/TC1-2008/0137 [79], and XSH/TC1-2008/0138 [14] are applied.

End of informative text.


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