c语言学习 dos.h包括?

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#ifndef _DOS_H_
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#define _DOS_H_
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#include "pc.h"
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union REGS {
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struct {
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unsigned long ax;
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unsigned long bx;
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unsigned long cx;
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unsigned long dx;
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unsigned long si;
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unsigned long di;
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unsigned long cflag;
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unsigned long flags;
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} x;
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struct {
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unsigned char al;
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unsigned char ah;
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unsigned short upper_ax;
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unsigned char bl;
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unsigned char bh;
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unsigned short upper_bx;
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unsigned char cl;
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unsigned char ch;
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unsigned short upper_cx;
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unsigned char dl;
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unsigned char dh;
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unsigned short upper_dx;
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} h;
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};
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struct SREGS {
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unsigned short cs;
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unsigned short ds;
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unsigned short