vsprintf() - I/O Function

Tutorials

Cpp

Topic

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

Explanation

vsprintf() is an I/O function is used to write the contents of the format string to the stream, with a pointer to a list of arguments replacing the argument list. This function returns the totalnumber of characters, but on failure a negative value is returned.

Syntax:

    int vsprintf (char * str, const char * format, va_list arg );

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

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 <stdarg.h>
   #include <stdio.h>
   void vsform (char *string, char *format, ...);
   char arr [] = "%s  %s  %s\n";
   int main(void)
     {
      char string[100];
      vsform(string, arr , "A", "B", "C");
      printf("The strings are:  %s\n", string);
     }
   void vsform(char *string, char *fmt, ...)
     {
      va_list arg_ptr;
      va_start(arg_ptr, fmt);
      vsprintf(string, fmt, arg_ptr);
      va_end(arg_ptr);
     }

Result:setbufeg.txt

    The strings are:  A B C

In the above example the array "arr" is used to write the content to get the formatted output with multiple arguments.