C and pointers Chapter 18 runtime environment 18.8 programming exercises

1. Write an assembly language program for your system , It accepts 3 Integer parameters and return their sum . 
analysis ：
Leave it to be proved later ： 
2. Write an assembly language program , establish 3 An integer value and call printf The function prints them out .
analysis ：
Leave it to be proved later ：  
3. Assume stdarg.h The file was accidentally deleted from your file . Please write a group of 7 Described in Chapter stdarg macro .
analysis ：
The answer actually depends on the specific environment . However, the solution here applies to the environment discussed in this chapter . The user must provide the actual type of the parameter after the standard type conversion . real stdarg.h That's what macros do . 
/*
** Standard library files stdarg.h Alternatives to defined macros . 
*/ 
/*
** va_list
** Type a variable that holds a pointer to the variable part of the parameter list . What we use here is char *,
** Because the operations acting on them have not been adjusted .
*/
typdef char *va_list;

/*
** va_start
** Used to initialize a va_list Macro of variable , Make it point to... In the stack 1 A variable parameter . 
*/ 
#define va_start( arg_ptr, arg )  arg_ptr = (char *)&arg + sizeof(arg)

/*
** va_arg
** Macro used to return the value of the next variable in the stack , It increases at the same time arg_ptr Value , Make it point to the next parameter . 
*/
#define va_arg( arg_ptr, type ) *((type *)arg_ptr)++

/*
** va_end
** Called after the last access of the variable parameter . In this environment , It doesn't need to perform any tasks . 
*/ 
#define va_end( arg_ptr )