Implementation of vprintf() : C

[Adolfa]

Hello, I am student of the Bsc(Computer Science). I have the knowledge of the C language. I have the C programming language in the syllabus. I have the knowledge about C language. But I did not much in detail about the C language. I have to submit the assignment on vprintf() function as suggested by the professor. I know about the printf() function. But I did not know about the vprintf() function. So, I want to know what is vprintf() function, How can they be used in the program, and what is the difference between the vprintf() and printf() functions. Can anyone know about the vprintf() function.

[Praetor]

Using an argument list, This vprintf() function sends formatted output to stdio. The vprintf() function is the same as the printf() function except that vprintf() function prints a number of values from a variable argument list. I think It is good enough for you to know about the vprintf() function. The following is the syntax of the vprintf() function :
#include <stdio.h>
#include <stdarg.h>
int vprintf( const char *frmt, v_lst arg );

[Modifier]

I think you know at least about the Library functions of C language. Under control of the argument format, this vprintf() function writes output to the file stdout. The format string is described under the description of the printf() function. With the variable argument list replaced with arg, this vprintf() function can be an equivalent to the printf() function that which has been initialized by the va_start() macro. This vprintf() function returns the number of characters or a negative value if there is output an error occurred. The errno indicates that the error is detected, If an error occurs.

[MindSpace]

The following shows the use of vprintf() in a general error message routine:
#include <stdio.h>
#include <stdarg.h>
void ermg( char *frmt, ... )
{
v_lst arglst;

printf( "Error: " );
v_start( arglst, frmt );
vprintf( frmt, arglst );
v_end( arglst );
}
void main()
{
ermg( "%s %d %s", "Failed", 100, "times" );
}

[Reegan]

There is another one more example of vprintf() function :
#include <stdarg.h>
#undef OPTIMIZE
#include <crtdll/stdio.h>
#include <crtdll/wchar.h>
#undef vprintf
#undef vwprintf
int vprintf (frmt, ag)
const char *frmt;
v_lst ag;
{
int rt = vfprintf (stdout, frmt, ag);
fflush(stdout);
return rt;
}