How printf() works ??

anyone can explain me...How printf() function works.

there any way to find out the coding of any library function in Turbo C??

 

To get the code for Turbo C library functions you need to use tlib (included with turboc) - extract the function from the corresponding library (.lib file in directory lib) - disassemble to get an assembly language listing - I do not know if a better tool is available.

As to how printf works I am appending the foll program - I am also enclosing as zip file

Code:

#include <stdio.h>
#include <stdarg.h>
#include <string.h>

/*
http://msdn.microsoft.com/en-us/library/kb57fad8%28v=vs.71%29.aspx 
I used the above link for this example - to get the method of picking trailing args from the stack
*/
void display_int(int d);
void demo_printf(char *narration, ...); /* use ONLY 3 '.' i.e.  ... */
void display_str(char *s);

void main()
{
	demo_printf("the value of %s is between %d and %d\n***", "PI", 3, 4);
}

/* our toy implementation of printf */
void demo_printf(char *narration, ...) /* use ONLY 3 '.' i.e.  ... to denote variable no of trailing arguments*/
{
	/* this illustrates use of only %s, %d and \n */
	va_list argptr;
	char *ptr;
	int d, i;
	
	va_start(argptr, narration);
	
	for( i = 0; i < strlen(narration); i++ )
	{
		if( narration[ i ] != '%' && narration[ i ] != '\\' )
			putc(narration[ i ], stdout);
		else if( narration[ i ] == '%' )
		{
			if( narration[ i + 1 ] == 'd' )
			{
				d = va_arg(argptr, int);
				display_int(d);
				i++; /* skip next char in for loop */
			}
			else if( narration[ i + 1 ] == 's' )
			{
				ptr = va_arg(argptr, char *);
				display_str(ptr);
				i++; /* skip next char in for loop */
			}
		}
		else if( narration[ i + 1 ] == 'n' )
		{
			putc('\n', stdout);
			i++;
		}
	}
	
	va_end(argptr);
	
}

void display_str(char *s)
{
	int i;
	
	for( i = 0; i < strlen(s); i++ )
		putc(s[ i ], stdout);
	
}

void display_int(int d)
{
	char intstr[ 15 ];
	int i;
	
	i = sizeof(intstr) - 1;
	intstr[ i-- ] = 0; /* null terminate*/
	for( ; i >= 0 && d; i-- )
	{
		intstr[ i ] = '0' + d % 10;
		d /= 10;
	}
	i++; /* to offset last decrement in for loop */
	
	display_str(intstr + i);
}

 

We have a basic tutorial on How Format String Functions work , You can have a look.

 

I helps to print what ever is typed between inverted comas.

 

its not clear to me....please explain