vfprintf() - I/O function

Tutorials

Cpp

Topic

How is "vfprintf()" used in C++?

Explanation

vfprintf() is an I/O function that writes the contents of the format string to an array, with a pointer to a list of arguments replacing the argument list. This function returns the total number of characters, but on failure a negative value is returned.

Syntax:

    int vfprintf ( FILE * stream, const char * format, va_list arg );

The following table lists the type specifier used with vfprintf()

Type	Description
c	Character
d or i	Signed decimal integer
e	Scientific notation using e character
E	Scientific notation using E character
f	Decimal floating point
g	Use the shorter of %e or %f
G	Use the shorter of %E or %f
o	Signed octal
s	String of characters
u	Unsigned decimal integer
x	Unsigned hexadecimal integer
X	Unsigned hexadecimal integer(capital)
p	Pointer address
%	A % followed by another % character will write % to the stream.

Example:

   #include <stdio.h>
   #include <stdarg.h>
   void Form (FILE *str, char * format, ...)
    {
      va_list args;
      va_start (args, format);
      vfprintf (str,format, args);
      va_end (args);
    }
   int main ()
    {
      FILE * str;
      str = fopen ("vfprintf.txt","w");
      Form (str,"With only one argumet %f \n",1.0);
      Form (str,"With two arguments %d , %s.\n",2,"arguments");
      fclose(str);
      return 0;
    }

Result:vfprintf.txt

    With one floating point argumet:: 1.000000
    With decimal, string argument:: 2 , asddasd.

In the above example the contents are written to a stream "str" with single, multiple arguments.

vfprintf() - I/O Function