Structural example
#include <iostream>
#include <vector>
using namespace std;
// The 'Context' class
class Context {
};
// The 'AbstractExpression' abstract class
class AbstractExpression {
public:
virtual void Interpret(Context *context) = 0;
};
// The 'TerminalExpression' class
class TerminalExpression : public AbstractExpression {
public:
virtual void Interpret(Context *context) {
cout << "Called Terminal.Interpret()" << endl;
}
};
// The 'NonterminalExpression' class
class NonterminalExpression : public AbstractExpression {
public:
virtual void Interpret(Context *context) {
cout << "Called Nonterminal.Interpret()" << endl;
}
};
// Entry point into console application.
int main() {
Context *context = new Context;
// Usually a tree
vector<AbstractExpression*> list;
// Populate 'abstract syntax tree'
list.push_back(new TerminalExpression);
list.push_back(new NonterminalExpression);
list.push_back(new TerminalExpression);
list.push_back(new TerminalExpression);
vector<AbstractExpression*>::iterator it;
// Interpret
it = list.begin();
while (it != list.end()) {
(*it)->Interpret(context);
++it;
}
// end
it = list.begin();
while (it != list.end()) {
delete *it;
++it;
}
return 0;
}
Real World example
#include <iostream>
#include <string>
#include <list>
using namespace std;
// The 'Context' class
class Context {
private:
string _input;
int _output;
public:
// Constructor
Context(const string &input) {
_input = input;
_output = 0;
}
// Gets or sets input
string getInput() {
return _input;
}
void setInput(const string &value) {
_input = value;
}
// Gets or sets output
int getOutput() {
return _output;
}
void setOutput(int value) {
_output = value;
}
};
// The 'AbstractExpression' class
class Expression {
public:
void Interpret(Context *context) {
if (context->getInput().length() == 0) {
return;
}
if (context->getInput().compare(0, Nine().length(), Nine()) == 0) {
context->setOutput(context->getOutput() + (9 * Multiplier()));
context->setInput(context->getInput().substr(2));
}
else if (context->getInput().compare(0, Four().length(), Four()) == 0) {
context->setOutput(context->getOutput() + (4 * Multiplier()));
context->setInput(context->getInput().substr(2));
}
else if (context->getInput().compare(0, Five().length(), Five()) == 0) {
context->setOutput(context->getOutput() + (5 * Multiplier()));
context->setInput(context->getInput().substr(1));
}
while (context->getInput().compare(0, One().length(), One()) == 0) {
context->setOutput(context->getOutput() + (1 * Multiplier()));
context->setInput(context->getInput().substr(1));
}
}
virtual string One() = 0;
virtual string Four() = 0;
virtual string Five() = 0;
virtual string Nine() = 0;
virtual int Multiplier() = 0; // multiplier: 掛ける、増える
};
// A 'TerminalExpression' class
// Thousand checks for the Roman Numeral M
class ThousandExpression : public Expression {
public:
virtual string One() { return "M"; }
virtual string Four() { return " "; }
virtual string Five() { return " "; }
virtual string Nine() { return " "; }
virtual int Multiplier() { return 1000; }
};
// A 'TerminalExpression' class
// Hundred checks C, CD, D or CM
class HundredExpression : public Expression {
public:
virtual string One() { return "C"; }
virtual string Four() { return "CD"; }
virtual string Five() { return "D"; }
virtual string Nine() { return "CM"; }
virtual int Multiplier() { return 100; }
};
// A 'TerminalExpression' class
// Ten checks for X, XL, L and XC
class TenExpression : public Expression {
public:
virtual string One() { return "X"; }
virtual string Four() { return "XL"; }
virtual string Five() { return "L"; }
virtual string Nine() { return "XC"; }
virtual int Multiplier() { return 10; }
};
// A 'TerminalExpression' class
// One checks for I, II, III, IV, V, VI,VII, VIII, IX
class OneExpression : public Expression {
public:
virtual string One() { return "I"; }
virtual string Four() { return "IV"; }
virtual string Five() { return "V"; }
virtual string Nine() { return "IX"; }
virtual int Multiplier() { return 1; }
};
// Entry point into console application.
int main() {
string roman = "MCMXXVIII";
Context *context = new Context(roman);
// Build the 'parse tree'
list<Expression*> tree;
tree.push_back(new ThousandExpression);
tree.push_back(new HundredExpression);
tree.push_back(new TenExpression);
tree.push_back(new OneExpression);
list<Expression*>::iterator it;
// Interpret
it = tree.begin();
while (it != tree.end()) {
(*it)->Interpret(context);
++it;
}
cout << roman << " = " << context->getOutput() << endl;
// end
it = tree.begin();
while (it != tree.end()) {
delete *it;
++it;
}
return 0;
}
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最終更新：2011年12月31日 23:25
