fwprintf, wprintf, swprintf Subroutines

Purpose

Print formatted wide-character output.

Library

Standard Library (libc.a)

Syntax

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

int fwprintf ( FILE * stream, const wchar_t * format, . . .)
int wprintf (const wchar_t * format, . .)
int swprintf (wchar_t *s, size_t n, const wchar_t * format, . . .)

Description

The fwprintf function places output on the named output stream. The wprintf function places output on the standard output stream stdout. The swprintf function places output followed by the null wide-character in consecutive wide-characters starting at *s; no more than n wide-characters are written, including a terminating null wide-character, which is always added (unless n is zero).

Each of these functions converts, formats and prints its arguments under control of the format wide-character string. The format is composed of zero or more directives: ordinary wide-characters, which are simply copied to the output stream and conversion specifications , each of which results in the fetching of zero or more arguments. The results are undefined if there are insufficient arguments for the format. If the format is exhausted while arguments remain, the excess arguments are evaluated but are otherwise ignored.

EX Conversions can be applied to the nth argument after the format in the argument list, rather than to the next unused argument. In this case, the conversion wide-character % (see below) is replaced by the sequence %n$, where n is a decimal integer in the range [1, {NL_ARGMAX}], giving the position of the argument in the argument list. This feature provides for the definition of format wide-character strings that select arguments in an order appropriate to specific languages (see the EXAMPLES section).

In format wide-character strings containing the %n$ form of conversion specifications, numbered arguments in the argument list can be referenced from the format wide-character string as many times as required.

In format wide-character strings containing the % form of conversion specifications, each argument in the argument list is used exactly once.

All forms of the fwprintf functions allow for the insertion of a language-dependent radix character in the output string, output as a wide-character value. The radix character is defined in the program's locale (category LC_NUMERIC). In the POSIX locale, or in a locale where the radix character is not defined, the radix character defaults to a period (.).

EX Each conversion specification is introduced by the % wide-character or by the wide-character sequence %n$,after which the following appear in sequence:

• Zero or more flags (in any order), which modify the meaning of the conversion specification.
• An optional minimum field width. If the converted value has fewer wide-characters than the field width, it will be padded with spaces by default on the left; it will be padded on the right, if the left-adjustment flag (-), described below, is given to the field width. The field width takes the form of an asterisk (*), described below, or a decimal integer.
• An optional precision that gives the minimum number of digits to appear for the d, i, o, u, x and X conversions; the number of digits to appear after the radix character for the e, E and f conversions; the maximum number of significant digits for the g and G conversions; or the maximum number of wide-characters to be printed from a string in s conversions. The precision takes the form of a period (.) followed either by an asterisk (*), described below, or an optional decimal digit string, where a null digit string is treated as 0. If a precision appears with any other conversion wide-character, the behaviour is undefined.
• An optional l (ell) specifying that a following c conversion wide-character applies to a wint_t argument; an optional l specifying that a following s conversion wide-character applies to a wchar_t argument; an optional h specifying that a following d, i, o, u, x or X conversion wide-character applies to a type short int or type unsigned short int argument (the argument will have been promoted according to the integral promotions, and its value will be converted to type short int or unsigned short int before printing); an optional h specifying that a following n conversion wide-character applies to a pointer to a type short int argument; an optional l (ell) specifying that a following d, i, o, u, x or X conversion wide-character applies to a type long int or unsigned long int argument; an optional l (ell) specifying that a following n conversion wide-character applies to a pointer to a type long int argument; or an optional L specifying that a following e, E, f, g or G conversion wide-character applies to a type long double argument. If an h, l or L appears with any other conversion wide-character, the behavior is undefined.
• A conversion wide-character that indicates the type of conversion to be applied.

A field width, or precision, or both, may be indicated by an asterisk (*). In this case an argument of type int supplies the field width or precision. Arguments specifying field width, or precision, or both must appear in that order before the argument, if any, to be converted. A negative field width is taken as a - flag followed by a positive field width. A negative precision is taken as if EX the precision were omitted. In format wide-character strings containing the %n$ form of a conversion specification, a field width or precision may be indicated by the sequence *m$, where m is a decimal integer in the range [1, {NL_ARGMAX}] giving the position in the argument list (after the format argument) of an integer argument containing the field width or precision, for example:

 wprintf(L"%1$d:%2$.*3$d:%4$.*3$d\n", hour, min, precision, sec);

The format can contain either numbered argument specifications (that is, %n$ and *m$), or unnumbered argument specifications (that is, % and *), but normally not both. The only exception to this is that %% can be mixed with the %n$ form. The results of mixing numbered and unnumbered argument specifications in a format wide-character string are undefined. When numbered argument specifications are used, specifying the Nth argument requires that all the leading arguments, from the first to the (N-1)th, are specified in the format wide-character string.

The flag wide-characters and their meanings are:

The conversion wide-characters and their meanings are:

If a conversion specification does not match one of the above forms, the behavior is undefined.

In no case does a non-existent or small field width cause truncation of a field; if the result of a conversion is wider than the field width, the field is simply expanded to contain the conversion result. Characters generated by fwprintf and wprintf are printed as if fputwc had been called.

The st_ctime and st_mtime fields of the file will be marked for update between the call to a successful execution of fwprintf or wprintf and the next successful completion of a call to fflush or fclose on the same stream or a call to exit or abort.

Return Values

Upon successful completion, these functions return the number of wide-characters transmitted excluding the terminating null wide-character in the case of swprintf or a negative value if an output error was encountered.

Error Codes

For the conditions under which fwprintf and wprintf will fail and may fail, refer to fputwc .In addition, all forms of fwprintf may fail if:

Examples

To print the language-independent date and time format, the following statement could be used:

 wprintf (format, weekday, month, day, hour, min);

For American usage, format could be a pointer to the wide-character string:

 L"%s, %s %d, %d:%.2d\n"

producing the message:

 Sunday, July 3, 10:02

whereas for German usage, format could be a pointer to the wide-character string:

L"%1$s, %3$d. %2$s, %4$d:%5$.2d\n"

producing the message:

 Sonntag, 3. July, 10:02

Implementation Specifics

These subroutines are part of Base Operating System (BOS) subroutines.

Related Information

The btowc subroutine.

The fputwc subroutine.

The fwscanf subroutine.

The setlocale subroutine.

The mbrtowc subroutine.

The stdio.h file.

The wchar.h file.

The XBD specification, Chapter 5, Locale.