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# std::wprintf, std::fwprintf, std::swprintf

From cppreference.com
< cpp‎ | io‎ | c

Defined in header `<cwchar>` |  |
int wprintf( const wchar_t* format, ... ); | (1) |
int fwprintf( std::FILE* stream, const wchar_t* format, ... ); | (2) |
int swprintf( wchar_t* buffer, std::size_t size, const wchar_t* format, ... ); | (3) |

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) Writes the results to a wide string `buffer`. At most size-1 wide characters are written. The resulting wide character string will be terminated with a null character, unless `size` is zero.

### [edit] Parameters

stream | - | output file stream to write to
buffer | - | pointer to a wide character string to write to
size | - | up to `size - 1` characters may be written, plus the null terminator
format | - | pointer to a null-terminated wide string specifying how to interpret the data. The format string consists of ordinary characters (except `%`), which are copied unchanged into the output stream, and conversion specifications. Each conversion specification has the following format: introductory `%` character (optional) one or more flags that modify the behavior of the conversion: `-`: 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. `0` : for integer and floating point number conversions, leading zeros are used to pad the field instead of space characters. For floating point 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. (optional) integer value or `*` that specifies minimum field width. The result is padded with space characters (by default), if required, on the left when right-justified, or on the right if left-justified. In the case when `*` is used, the width is specified by an additional argument of type int. If the value of the argument is negative, it results with the `-` flag specified and positive field width. (optional) `.` followed by integer number or `*` that specifies precision of the conversion. In the case when `*` is used, the precision is specified by an additional argument of type int. If the value of this argument is negative, it is ignored. See the table below for exact effects of precision. (optional) length modifier that specifies the size of the argument conversion format specifier The following format specifiers are available:
Conversion specifier | Explanation | Argument type
--- | --- | ---
length modifier | `hh` | `h` | (none) | `l` | `ll` | `j` | `z` | `t` | `L`
`%` | 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. The argument is first converted to unsigned char. If the l modifier is used, the argument is first converted to a character string as if by %ls with a wchar_t[2] argument. | N/A | N/A | int | wint_t | N/A | N/A | N/A | N/A | N/A
`s` | writes a character string The argument must be a pointer to the initial element of an array of characters. Precision specifies the maximum number of bytes to be written. If Presition is not specified, writes every byte up to and not including the first null terminator. If the l specifier is used, the argument must be a pointer to the initial element of an array of wchar_t, which is converted to char array as if by a call to std::wcrtomb with zero-initialized conversion state. | 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. Precision specifies the minimum number of digits to appear. The default precision is 1. If both the converted value and the precision are ​0​ the conversion results in no characters. | signed char | short | int | long | long long | intmax_t | signed size_t | ptrdiff_t | N/A
`o` | converts a unsigned integer into octal representation oooo. Precision specifies the minimum number of digits to appear. The default precision is 1. If both the converted value and the precision are ​0​ the conversion results in no characters. In the alternative implementation precision is increased if necessary, to write one leading zero. In that case if both the converted value and the precision are ​0​, single ​0​ is written. | 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. For the `x` conversion letters `abcdef` are used. For the `X` conversion letters `ABCDEF` are used. Precision specifies the minimum number of digits to appear. The default precision is 1. If both the converted value and the precision are ​0​ the conversion results in no characters. In the alternative implementation `0x` or `0X` is prefixed to results if the converted value is nonzero. | N/A
`u` | converts an unsigned integer into decimal representation dddd. Precision specifies the minimum number of digits to appear. The default precision is 1. If both the converted value and the precision are ​0​ the conversion results in no characters. | N/A
`f` `F` | converts floating-point number to the decimal notation in the style [-]ddd.ddd. Precision specifies the minimum number of digits to appear after the decimal point character. The default precision is 6. In the alternative implementation decimal point character is written even if no digits follow it. For infinity and not-a-number conversion style see notes. | N/A | N/A | double | no effect | N/A | N/A | N/A | N/A | long double
`e` `E` | converts floating-point number to the decimal exponent notation. For the `e` conversion style [-]d.ddd`e`±dd is used. For the `E` conversion style [-]d.ddd`E`±dd is used. The exponent contains at least two digits, more digits are used only if necessary. If the value is ​0​, the exponent is also ​0​. Precision specifies the minimum number of digits to appear after the decimal point character. The default precision is 6. In the alternative implementation decimal point character is written even if no digits follow it. For infinity and not-a-number conversion style see notes. | N/A | N/A | N/A | N/A | N/A | N/A
`a` `A` | converts floating-point number to the hexadecimal exponent notation. For the `a` conversion style [-]`0x`h.hhh`p`±d is used. For the `A` conversion style [-]`0X`h.hhh`P`±d is used. The first hexadecimal digit is `0` if the argument is not a normalized floating point value. If the value is ​0​, the exponent is also ​0​. Precision specifies the minimum number of digits to appear after the decimal point character. The default precision is sufficient for exact representation of the value. In the alternative implementation decimal point character is written even if no digits follow it. For infinity and not-a-number conversion style see notes. | 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. For the `g` conversion style conversion with style `e` or `f` will be performed. For the `G` conversion style conversion with style `E` or `F` will be performed. Let `P` equal the precision if nonzero, 6 if the precision is not specified, or 1 if the precision is ​0​. Then, if a conversion with style `E` would have an exponent of `X`: if P > X ≥ −4, the conversion is with style `f` or `F` and precision P − 1 − X. otherwise, the conversion is with style `e` or `E` and precision P − 1. Unless alternative representation is requested the trailing zeros are removed, also the decimal point character is removed if no fractional part is left. For infinity and not-a-number conversion style see notes. | 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. The result is written to the value pointed to by the argument. The complete specification must be `%n`. | signed char* | short* | int* | long* | long long* | intmax_t* | signed size_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. Even though `%c` expects `int` argument, it is safe to pass a `char` because of the integer promotion that takes place when a variadic function is called The correct conversion specifiers for the fixed-width character types (std::int8_t, etc) are defined in the header <cinttypes>
... | - | arguments specifying data to print

### [edit] Return value

Number of wide characters written if successful (not counting the terminating null character) or negative value if an error occurred.

### [edit] Example

Run this code

    #include <iostream>
    #include <locale>
    #include <clocale>
    #include <cwchar>

    int main()
    {
        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
        std::setlocale(LC_ALL, "en_US.utf8");

        std::swprintf(warr, sizeof warr/sizeof *warr,
                      L"Converted from UTF-8: '%s'", narrow_str);

        std::wcout.imbue(std::locale("en_US.utf8"));
        std::wcout << warr << '\n';
    }

Output:

    Converted from UTF-8: 'zß水🍌'

### [edit] See also

vwprintfvfwprintfvswprintf | prints formatted wide character output to stdout, a file stream or a buffer using variable argument list (function) [edit]
fputws | writes a wide string to a file stream (function) [edit]
C documentation for wprintf, fwprintf, swprintf

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