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Showing content from https://en.cppreference.com/w/cpp/language/../algorithm/../../cpp/../c/io/fwprintf.html below:

wprintf, fwprintf, swprintf, wprintf_s, fwprintf_s, swprintf_s, snwprintf_s

(1)

int wprintf( const wchar_t* format, ... );

(since C95)
(until C99)

int wprintf( const wchar_t* restrict format, ... );

(since C99) (2) int fwprintf( FILE* stream, const wchar_t* format, ... ); (since C95)
(until C99) int fwprintf( FILE* restrict stream,
              const wchar_t* restrict format, ... ); (since C99) (3) int swprintf( wchar_t* buffer, size_t bufsz,
              const wchar_t* format, ... ); (since C95)
(until C99) int swprintf( wchar_t* restrict buffer, size_t bufsz,
              const wchar_t* restrict format, ... ); (since C99)

int wprintf_s( const wchar_t* restrict format, ... );

(4) (since C11) int fwprintf_s( FILE* restrict stream,
                const wchar_t* restrict format, ... ); (5) (since C11)

int swprintf_s( wchar_t* restrict buffer, rsize_t bufsz,
                const wchar_t* restrict format, ... );

(6) (since C11)

int snwprintf_s( wchar_t* restrict s, rsize_t n,
                 const wchar_t* restrict format, ... );

(7) (since C11)

Loads the data from the given locations, converts them to wide string equivalents and writes the results to a variety of sinks.

1)

Writes the results to

stdout

.

2) Writes the results to a file stream stream.

3) If bufsz is greater than zero, writes the results to a wide string buffer. At most bufsz - 1 wide characters are written followed by null wide character. If bufsz is zero, nothing is written (and buffer may be a null pointer).

4-6)

Same as

(1-3)

, except that the following errors are detected at runtime and call the currently installed

constraint handler

function:

7)

Same as

(6)

, except it will truncate the result to fit within the array pointed to by s.

As with all bounds-checked functions, wprintf_s, fwprintf_s, swprintf_s, and snwprintf_s are only guaranteed to be available if __STDC_LIB_EXT1__ is defined by the implementation and if the user defines __STDC_WANT_LIB_EXT1__ to the integer constant 1 before including <stdio.h>.
[edit] Parameters stream - output file stream to write to buffer - pointer to a wide character string to write to bufsz - up to bufsz - 1 wide characters may be written, plus the null terminator format - pointer to a null-terminated wide string specifying how to interpret the data ... - arguments specifying data to print. If any argument after default argument promotions is not the type expected by the corresponding conversion specifier, or if there are fewer arguments than required by format, the behavior is undefined. If there are more arguments than required by format, the extraneous arguments are evaluated and ignored.


The format string consists of ordinary wide characters (except %), which are copied unchanged into the output stream, and conversion specifications. Each conversion specification has the following format:

  • -: the result of the conversion is left-justified within the field (by default it is right-justified).
  • +: the sign of signed conversions is always prepended to the result of the conversion (by default the result is preceded by minus only when it is negative).
  • space: if the result of a signed conversion does not start with a sign character, or is empty, space is prepended to the result. It is ignored if + flag is present.
  • #: alternative form of the conversion is performed. See the table below for exact effects otherwise the behavior is undefined.
  • 0: for integer and floating-point number conversions, leading zeros are used to pad the field instead of space characters. For integer numbers it is ignored if the precision is explicitly specified. For other conversions using this flag results in undefined behavior. It is ignored if - flag is present.

The following format specifiers are available:

Conversion
Specifier Explanation Expected
Argument Type Length Modifier→ hh h none l ll j z t L Only available since C99→ Yes Yes Yes Yes Yes % Writes literal %. The full conversion specification must be %%. N/A N/A N/A N/A N/A N/A N/A N/A N/A c

Writes a single character.

N/A N/A

int

wint_t

N/A N/A N/A N/A N/A s

Writes a character string.

N/A N/A

char*

wchar_t*

N/A N/A N/A N/A N/A d
i

Converts a signed integer into decimal representation [-]dddd.

signed char

short

int

long

long long

intmax_t

※

ptrdiff_t N/A o

Converts an unsigned integer into octal representation oooo.

unsigned char

unsigned short

unsigned int

unsigned long

unsigned long long

uintmax_t size_t

unsigned version of

ptrdiff_t N/A x
X

Converts an unsigned integer into hexadecimal representation hhhh.

N/A u

Converts an unsigned integer into decimal representation dddd.

N/A f
F (C99)

Converts floating-point number to the decimal notation in the style [-]ddd.ddd.

N/A N/A

double

double (C99)

N/A N/A N/A N/A

long double

e
E

Converts floating-point number to the decimal exponent notation.

N/A N/A N/A N/A N/A N/A a
A

(C99)

Converts floating-point number to the hexadecimal exponent notation.

N/A N/A N/A N/A N/A N/A g
G

Converts floating-point number to decimal or decimal exponent notation depending on the value and the precision.

N/A N/A N/A N/A N/A N/A n

Returns the number of characters written so far by this call to the function.

signed char*

short*

int*

long*

long long*

intmax_t*

※

 ptrdiff_t*  N/A p

Writes an implementation defined character sequence defining a pointer.

N/A N/A

void*

N/A N/A N/A N/A N/A N/A Notes

The floating-point conversion functions convert infinity to inf or infinity. Which one is used is implementation defined.

Not-a-number is converted to nan or nan(char_sequence). Which one is used is implementation defined.

The conversions F, E, G, A output INF, INFINITY, NAN instead.

The conversion specifier used to print char, unsigned char, signed char, short, and unsigned short expects promoted types of default argument promotions, but before printing its value will be converted to char, unsigned char, signed char, short, and unsigned short. It is safe to pass values of these types because of the promotion that takes place when a variadic function is called.

The correct conversion specifications for the fixed-width character types (int8_t, etc) are defined in the header <inttypes.h> (although PRIdMAX, PRIuMAX, etc is synonymous with %jd, %ju, etc).

The memory-writing conversion specifier %n is a common target of security exploits where format strings depend on user input and is not supported by the bounds-checked printf_s family of functions(since C11).

There is a sequence point after the action of each conversion specifier; this permits storing multiple %n results in the same variable or, as an edge case, printing a string modified by an earlier %n within the same call.

If a conversion specification is invalid, the behavior is undefined.

[edit] Return value

1,2) Number of wide characters written if successful or negative value if an error occurred.

3) Number of wide characters written (not counting the terminating null wide character) if successful or negative value if an encoding error occurred or if the number of characters to be generated was equal or greater than bufsz (including when bufsz is zero).

4,5) Number of wide characters written if successful or negative value if an error occurred.

6) Number of wide characters (not counting the terminating null) that were written to buffer. Returns a negative value on encoding errors and on overflow. Returns zero on all other errors.

7) Number of wide characters (not counting the terminating null) that would have been written to buffer had bufsz been sufficiently large, or a negative value if an error occurs. (meaning, write was successful and complete only if the return is nonnegative and less than bufsz)

[edit] Notes

While narrow strings provide snprintf, which makes it possible to determine the required output buffer size, there is no equivalent for wide strings (until snwprintf_s)(since C11), and in order to determine the buffer size, the program may need to call swprintf, check the result value, and reallocate a larger buffer, trying again until successful.

snwprintf_s, unlike swprintf_s, will truncate the result to fit within the array pointed to by buffer, even though truncation is treated as an error by most bounds-checked functions.

[edit] Example 
#include <locale.h>
#include <wchar.h>
 
int main(void)
{
    char narrow_str[] = "z\u00df\u6c34\U0001f34c";
                  // or "zß水🍌"
                  // or "\x7a\xc3\x9f\xe6\xb0\xb4\xf0\x9f\x8d\x8c";
    wchar_t warr[29]; // the expected string is 28 characters plus 1 null terminator
    setlocale(LC_ALL, "en_US.utf8");
    swprintf(warr, sizeof warr / sizeof* warr,
             L"Converted from UTF-8: '%s'", narrow_str);
    wprintf(L"%ls\n", warr);
}

Output:

Converted from UTF-8: 'zß水🍌'
[edit] References
[edit] See also

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