面向对象版计算器（六）

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SymbolTable实现

接下来的任务是让表达式支持变量与函数。
如a=100
a+5+log(0)
这里变量名与函数都算是符号，所以要有一个表存储这些符号SymbolTable

SymbolTable实现：

SymbolTable.h:

#ifndef  _SYMBOL_TABLE_H_#define  _SYMBOL_TABLE_H_#include <map>#include <string>class SymbolTable{enum {IDNOTFOUND = 0xffffffff};public:SymbolTable():curId_(0){};unsigned int Add(const std::string& str);unsigned int Find(const std::string& str)const;void Clear();std::string GetSymbolName(unsigned int id)const;~SymbolTable(void);private:std::map<const std::string,unsigned int> dictionary_;unsigned int curId_;};#endif

SymbolTabl.cpp:

#include "SymbolTable.h"#include <algorithm>SymbolTable::~SymbolTable(void){}unsigned int SymbolTable::Add(const std::string& str){dictionary_[str] = curId_;curId_++;}unsigned int SymbolTable::Find(const std::string& str)const{std::map<const std::string,unsigned int>::const_iterator it;it = dictionary_.find(str);if(it != dictionary_.end()){return it->second;}return IDNOTFOUND;}void SymbolTable::Clear(){dictionary_.clear();curId_ = 0;}//函数对象的用法  function object  functor(仿函数)//让一个类对象使用起来像一个函数  本质上是重载()运算符//stl六大组件之一//容器  算法 迭代器 适配器 函数对象  内存分配器对象class IsEqualId{public:explicit IsEqualId(unsigned int id):id_(id){}bool operator()(const std::pair<const std::string,unsigned int> &it)const{return it.second == id_;}private:unsigned int id_;};std::string SymbolTable::GetSymbolName(unsigned int id)const{std::map<const std::string,unsigned int>::const_iterator it;it = std::find_if(dictionary_.begin(),dictionary_.end(),IsEqualId(id));return it->first;}

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