std::wprintf

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

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 followed by null wide character.

Parameters

• introductory % character

The following format specifiers are available:

Conversion

specifier Explanation Argument type length modifier hh (C++11).

h (none) l ll (C++11).

j (C++11).

z (C++11).

t (C++11).

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 wchar_t as if by calling btowc. If the l modifier is used, the wint_t argument is first converted to wchar_t.

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 a character array containing a multibyte character sequence beginning in the initial shift state, which is converted to wide character array as if by a call to mbrtowc with zero-initialized conversion state. Precision specifies the maximum number of wide characters to be written. If Precision is not specified, writes every wide characters 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.

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

`double` (C++11) 

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.ddde±dd is used.

For the E conversion style -d.dddE±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 (C++11).

converts floating-point number to the hexadecimal exponent notation. For the a conversion style -0xh.hhhp±d is used.

For the A conversion style -0Xh.hhhP±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.

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 specification may not contain any flag, field width, or precision.

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 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 specifications for the fixed-width character types (int8_t, etc) are defined in the header <cinttypes> (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.

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.

 ...   -   arguments specifying data to print   

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 size (including when size is zero)

Notes

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

Example

​

#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?'

​

See also

| C documentation for wprintf, fwprintf, swprintf |

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