< 自己动手写操作系统>>这本书的完整源代码

				
				/*++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
				                              printf.c
				++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
				                                                    Forrest Yu, 2005
				++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++*/
				
				#include "type.h"
				#include "const.h"
				
				/******************************************************************************************
				                        可变参数函数调用原理（其中涉及的数字皆为举例）
				===========================================================================================
				
				i = 0x23;
				j = 0x78;
				char fmt[] = "%x%d";
				printf(fmt, i, j);
				
				        push    j
				        push    i
				        push    fmt
				        call    printf
				        add     esp, 3 * 4
				
				
				                ┃        HIGH        ┃                        ┃        HIGH        ┃
				                ┃        ...         ┃                        ┃        ...         ┃
				                ┣━━━━━━━━━━┫                        ┣━━━━━━━━━━┫
				                ┃                    ┃                 0x32010┃        '\0'        ┃
				                ┣━━━━━━━━━━┫                        ┣━━━━━━━━━━┫
				         0x3046C┃        0x78        ┃                 0x3200c┃         d          ┃
				                ┣━━━━━━━━━━┫                        ┣━━━━━━━━━━┫
				   arg = 0x30468┃        0x23        ┃                 0x32008┃         %          ┃
				                ┣━━━━━━━━━━┫                        ┣━━━━━━━━━━┫
				         0x30464┃      0x32000 ───╂────┐       0x32004┃         x          ┃
				                ┣━━━━━━━━━━┫        │              ┣━━━━━━━━━━┫
				                ┃                    ┃        └──→ 0x32000┃         %          ┃
				                ┣━━━━━━━━━━┫                        ┣━━━━━━━━━━┫
				                ┃        ...         ┃                        ┃        ...         ┃
				                ┃        LOW         ┃                        ┃        LOW         ┃
				
				实际上，调用 vsprintf 的情形是这样的：
				
				        vsprintf(buf, 0x32000, 0x30468);
				
				******************************************************************************************/
				
				/*======================================================================*
				                                 printf
				 *======================================================================*/
				int printf(const char *fmt, ...)
				{
					int i;
					char buf[256];
				
					va_list arg = (va_list)((char*)(&fmt) + 4);        /* 4 是参数 fmt 所占堆栈中的大小 */
					i = vsprintf(buf, fmt, arg);
					write(buf, i);
				
					return i;
				}