表达式 《c＋＋沉思录》第八章

1. /*
2. *=====================================================================================
3. *
4. *Filename:eval.cpp
5. *
6. *Description:表达式，《c＋＋沉思录》第8章
7. *
8. *Version:1.0
9. *Created:2009年01月07日15时51分53秒
10. *Revision:none
11. *Compiler:gcc
12. *
13. *Author:LiWeiJian(mn),lwj1396@163.com
14. *Company:hunanuniversity
15. *
16. *=====================================================================================
17. */
19. #include<iostream>
20. #include<string>
22. usingnamespacestd;
24. classExpr_node
25. {
27. friendclassExpr;
29. intuse;//引用计数
31. public:
32. virtualvoidprint(ostream&)const=0;
33. virtualintdocompute()const=0;
34. protected:
35. Expr_node():use(1)
36. {
37. //cout<<"Expr_node(),use="<<use<<endl;
38. }
39. virtual~Expr_node()
40. {
41. //cout<<"~Expr_node()"<<this<<endl;
42. }
43. };
46. classExpr
47. {
48. friendostream&operator<<(ostream&,constExpr&);
50. Expr_node*p;
52. public:
53. Expr(int);//创建一个Int_node
54. Expr(conststring&,Expr);//创建一个Unary_node
55. Expr(conststring&,Expr,Expr);//创建一个Binary_node
58. Expr(constExpr&t)
59. {
60. t.p->use++;
61. //构造与赋值不一样
62. //if(--p->use==0)
63. //deletep;
64. p=t.p;
65. //cout<<"Expr"<<this<<"的use="<<p->use<<endl;
66. }
68. Expr&operator=(constExpr&);
69. ~Expr()
70. {
71. if(--p->use==0)
72. {
73. //cout<<"~Expr()"<<this<<endl;
74. deletep;
75. }
76. }
78. intcompute()const
79. {
80. returnp->docompute();
81. }
82. };
84. classInt_node:publicExpr_node
85. {
86. friendclassExpr;
88. intn;
90. Int_node(intk):n(k){}
91. voidprint(ostream&o)const{o<<n;}
92. intdocompute()const{returnn;}
94. };
96. classUnary_node:publicExpr_node
97. {
98. friendclassExpr;
99. stringop;
100. Expropnd;
102. Unary_node(conststring&a,Exprb):
103. op(a),opnd(b)
104. {
105. }
107. voidprint(ostream&o)const
108. {
109. o<<"("<<op<<opnd<<")";
110. }
112. intdocompute()const
113. {
114. //暂定只能是负号
115. if(op=="-")
116. return-opnd.compute();
117. elseif(op=="+")
118. return+opnd.compute();
119. else
120. cout<<"error"<<endl;
121. return-1;
122. }
123. };
125. classBinary_node:publicExpr_node
126. {
127. friendclassExpr;
128. stringop;
129. Exprleft;
130. Exprright;
132. Binary_node(conststring&a,Exprb,Exprc):
133. op(a),left(b),right(c)
134. {
135. }
137. voidprint(ostream&o)const
138. {
139. o<<"("<<left<<op<<right<<")";
140. }
142. intdocompute()const
143. {
144. intleftval=left.compute();
145. intrightval=right.compute();
146. if(op=="-")returnleftval-rightval;
147. if(op=="+")returnleftval+rightval;
148. if(op=="*")returnleftval*rightval;
149. if(op=="/"&&rightval!=0)returnleftval/rightval;
150. return-1;
151. }
152. };
156. Expr::Expr(intn)
157. {
158. //cout<<"Expr("<<n<<")"<<endl;
159. p=newInt_node(n);
160. //cout<<"Expr的地址"<<this<<endl;
161. //cout<<"expr.expr_node的地址:"<<p<<endl;
162. }
164. Expr::Expr(conststring&op,Exprt)
165. {
166. //cout<<"Expr("<<op<<""<<t<<")"<<endl;
167. p=newUnary_node(op,t);
168. //cout<<"Expr的地址"<<this<<endl;
169. //cout<<"expr.expr_node的地址:"<<p<<endl;
171. }
173. Expr::Expr(conststring&op,Exprleft,Exprright)
174. {
175. //cout<<"Expr("<<left<<""<<op<<""<<right<<")"<<endl;
176. p=newBinary_node(op,left,right);
177. //cout<<"Expr的地址"<<this<<endl;
178. //cout<<"expr.expr_node的地址:"<<p<<endl;
180. }
182. Expr&
183. Expr::operator=(constExpr&rhs)
184. {
185. rhs.p->use++;
186. if(--p->use==0)
187. deletep;
188. p=rhs.p;
189. return*this;
190. }
192. ostream&operator<<(ostream&o,constExpr&e)
193. {
194. e.p->print(o);
195. returno;
196. }
200. intmain()
201. {
202. Expre=Expr("*",Expr("+",8,7),Expr("/",56,7));
203. cout<<e<<"="<<e.compute()<<endl;
204. }