NAME

fgetwc — get a wide-character code from a stream

SYNOPSIS

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

wint_t fgetwc(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.1-2024 defers to the ISO C standard.

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] 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().

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

RETURN VALUE

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 an error other than an encoding error occurs, the error indicator for the stream shall be set, and fgetwc() shall return WEOF ^[CX]  and shall set errno to indicate the error. If an encoding error occurs, ^[CX]  the error indicator for the stream shall be set, and fgetwc() shall return WEOF and shall set errno to indicate the error.

ERRORS

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

[EAGAIN]

^[CX] The O_NONBLOCK flag is set for the file descriptor underlying stream and the thread would be delayed in the fgetwc() operation.

[EBADF]

^[CX] The file descriptor underlying stream is not a valid file descriptor open for reading.

[EILSEQ]

The data obtained from the input stream does not form a valid character.

[EINTR]

^[CX] The read operation was terminated due to the receipt of a signal, and no data was transferred.

[EIO]

^[CX] 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.

[EOVERFLOW]

^[CX] The file is a regular file and an attempt was made to read at or beyond the offset maximum associated with the corresponding stream.

The fgetwc() function may fail if:

[ENOMEM]

^[CX] Insufficient storage space is available.

[ENXIO]

^[CX] A request was made of a nonexistent device, or the request was outside the capabilities of the device.

EXAMPLES

None.

APPLICATION USAGE

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

RATIONALE

The requirement to set the error indicator when an encoding error occurs is shaded CX because this is not required by the ISO C standard. However, the next revision of the ISO C standard is expected to add this requirement.

FUTURE DIRECTIONS

None.

SEE ALSO

2.5 Standard I/O Streams, feof, ferror, fopen

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>.

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:

• The [EIO] and [EOVERFLOW] mandatory error conditions are added.

• The [ENOMEM] and [ENXIO] optional error conditions are added.

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.

Issue 8

Austin Group Defect 1624 is applied, changing the RETURN VALUE and RATIONALE sections.