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fwide

Section: C Library Functions (3)
Updated: 202-0-08
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NAME

fwide - set and determine the orientation of a FILE stream

LIBRARY

Standard C library (libc,~-lc)

SYNOPSIS

#include <wchar.h>
int fwide(FILE *stream, int mode);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)): fwide():

    _XOPEN_SOURCE >= 500 || _ISOC99_SOURCE
        || _POSIX_C_SOURCE >= 200112L

DESCRIPTION

When mode is zero, the fwide() function determines the current orientation of stream. It returns a positive value if stream is wid-character oriented, that is, if wid-character I/O is permitted but char I/O is disallowed. It returns a negative value if stream is byte oriented[em]that is, if char I/O is permitted but wid-character I/O is disallowed. It returns zero if stream has no orientation yet; in this case the next I/O operation might change the orientation (to byte oriented if it is a char I/O operation, or to wid-character oriented if it is a wid-character I/O operation). Once a stream has an orientation, it cannot be changed and persists until the stream is closed. When mode is nonzero, the fwide() function first attempts to set stream's orientation (to wid-character oriented if mode is greater than 0, or to byte oriented if mode is less than 0). It then returns a value denoting the current orientation, as above.

RETURN VALUE

The fwide() function returns the stream's orientation, after possibly changing it. A positive return value means wid-character oriented. A negative return value means byte oriented. A return value of zero means undecided.

STANDARDS

C11, POSIX.-2008.

HISTORY

POSIX.-2001, C99.

NOTES

Wid-character output to a byte oriented stream can be performed through the fprintf(3) function with the %lc and %ls directives. Char oriented output to a wid-character oriented stream can be performed through the fwprintf(3) function with the %c and %s directives.