The implementation of printf__c++ using variable parameter simulation in "C + +"

First, printf function
The printf () function is a formatted output function that is generally used to output information in a prescribed format to a standard output device.
Prototype
int printf (const char* format, [argument] ...); Defined in Stdio.h

More printf detailed See links: printf () function detailed http://gaoxiaodiao.com/p/1.html

second, how to simulate the implementation of printf Analysis:

printf ("Hello haohaosong!\n");

printf ("%s", "Welcome to My bolg\n");

printf ("hell%c\n", ' O ');

We found that the parameters of the printf function are indeterminate

You must use something else to resolve the argument :

Using STDARG macros to solve variable parameter problems

Header file:<stdarg.h>

va_list;

Type Va_arg (va_list arg_ptr, type);

void Va_end (Va_list arg_ptr);

void Va_start (Va_list arg_ptr, Prev_param); (ANSI version)

under VC6.0, we go to the definition of the definition, which can be clearly found:

parsing:

Va_list is a macro-defined identifier that is a pointer to a character type

Va_start (ap,v) Remove the address of the variable that va_list defines, plus the number of variable elements

Va_arg (ap,t) takes the pointer to the content each time and moves the pointer back inside the macro

Va_end (AP) points The original pointer to null to prevent the occurrence of wild pointers three, specific code blocks:

#include <stdio.h>
#include <stdarg.h>
int my_printf (char* str,...)
{
	va_list arg;//defines the char* variable arg
	int count = 0;
	char* str_tmp = NULL;
	Va_start (ARG,STR),//For ARG initialization while
	(*str!= ' ")
	{	
		switch (*str) {case
			' C ':
				Putchar ( Va_arg (Arg,int));//Remove the character of a parameter and print the
				count++;
				break;
			Case ' s ':	
				str_tmp = (char*) va_arg (arg,int);//Remove the address of a parameter, because this is the string while
				(*str_tmp!= ' ")//Use the dereference for output
				{		
					Putchar (*str_tmp);
					count++;
					str_tmp++;	
				}
				break;
			Default:
				Putchar (*STR);	Not for ' C ' or ' s ', then print it directly
				count++;
				break;
		str++;		
	}
	Va_end (ARG);//point arg to NULL to prevent wild pointer return
	count;
}
int main ()
{	
	my_printf ("s CCC", "Hello", ' h ', ' h ', ' s ');
	return 0;
}

Run Result: