C++ fwprintf()

The fwprintf() function is defined in <cwchar> header file.

fwprintf() prototype

int fwprintf( FILE* stream, const wchar_t* format, ... );

The fwprintf() function writes the wide string pointed to by format to the file stream stream. The wide string format may contain format specifiers starting with % which are replaced by the values of variables that are passed to the fwprintf() function as additional arguments.

fwprintf() Parameters

• stream: Pointer to an output file stream where the contents are written.
• format: A pointer to a null terminated wide string that is written to stdout. It consists of wide characters along with optional format specifiers starting with %. The format specifiers are replaced by the values of respective variables that follows format.
  The format specifier has the following parts:
  • A leading % sign
  • Flags: Optional one or more flags that modifies the conversion behavior.
    • - : Left justify the result within the field. By default it is right justified.
    • + : The sign of the result is attached to the beginning of the value, even for positive results.
    • Space: If there is no sign, a space is attached to the beginning of the result.
    • # : An alternative form of the conversion is performed.
    • 0 : It is used for integer and floating point number. Leading zeros are used to pad the numbers instead of space.
  • Width: An optional * or integer value used to specify minimum width field.
  • Precision : An optional field consisting of a . followed by * or integer or nothing to specify the precision.
  • Length : An optional length modifier that specifies the size of the argument.
  • Specifier: A conversion format specifier. The available format specifiers are as follows:

  Format specifiers

  Format Specifier	Description
  %	Prints %
  c	Writes a single character
  s	Writes a character string
  d or i	Converts a signed integer to decimal representation
  o	Converts an unsigned integer to octal representation
  X or x	Converts an unsigned integer to hexadecimal representation
  u	Converts an unsigned integer to decimal representation
  F or f	Converts floating-point number to the decimal representation
  E or e	Converts floating-point number to the decimal exponent notation
  A or a	Converts floating-point number to the hexadecimal exponent
  G or g	Converts floating-point number to either decimal or decimal exponent notation
  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
  p	Writes an implementation defined character sequence defining a pointer.

  So the general format of format specifier is:

  %[flags][width][.precision][length]specifier

• … : Other additional arguments specifying the data to be written. They occur in a sequence according to the format specifier.

fwprintf() Return value

• On success, the fwprintf() function returns number of characters written.
• On failure it returns a negative value.

Example: How fwprintf() function works

#include <cwchar>
#include <cstdio>
#include <clocale>

int main()
{
	wchar_t hebrew_str[] = L"\u05D0 \u05D1 \u05E1 \u05D3 \u05EA";
	FILE *fp = fopen("example.txt","w");

	setlocale(LC_ALL, "en_US.UTF-8");
	fwprintf(fp, L"Here are some Hebrew letters: %ls", hebrew_str);
	fclose(fp);

	return 0;
}

When you run the program, the following will be written to example.txt:

Here are some Hebrew letters: א ב ס ד ת