从另一个类的构造函数调用方法C++

Question

我需要从另一个类的构造函数中的一个类调用一个方法。我不知道如何在没有得到“未在此范围内声明”错误的情况下执行此操作。注意我只是在学习C++。

请参阅symboltable.cpp中的评论，了解我在此尝试完成的内容。我不想找人为我做这件事。我可以使用一个例子或指出正确的方向，所以我可以弄清楚。

symboltable.h代码：

class SymbolTable 
{ 
public: 
    SymbolTable() {} 
    void insert(string variable, double value); 
    void insert(string variable); // added for additional insert method 
    double lookUp(string variable) const; 
    void init(); // Added as mentioned in the conference area. 
private: 
    struct Symbol 
    { 
     Symbol(string variable, double value) 
     { 
      this->variable = variable; 
      this->value = value; 
     } 
     string variable; 
     double value; 
    }; 
    vector<Symbol> elements; 
}; 

symboltable.cpp代码：

#include <string> 
#include <vector> 
#include <algorithm> 

using namespace std; 

#include "symboltable.h" 

/* Implementing the "unreferenced variable" warning. 
* Modify the symbol table by adding another insert method 
* that supplies only the variable name. 
* This method should be called when the variable name 
* is encountered while building the arithmetic expression tree. 
* It would be called in the constructor of the Variable class. 
* The existing insert method, which is called when an assignment is encountered, 
* would first check to see whether it is already in the symbol table. 
* If it is not, then it is unreferenced. 
*/ 

void SymbolTable::insert(string variable, double value) 
{ 
    /* This existing insert method, which is called when an assignment is encountered, 
    * first needs to check to see whether it is already in the symbol table. 
    * If it is not, then it is unreferenced. 
    * */ 

    //Need to check if variable is in the expression need to find out how the   expression is stored! 

if (find(elements.begin(), elements.end(), variable)) { 
    const Symbol& symbol = Symbol(variable, value); 
     elements.push_back(symbol); 
    } else 
     throw string("Error: Test for output"); 
} 

/* Adding another insert method that supplies only the variable name. 
* This method should be called when the variable name is encountered 
* while building the arithmetic expression tree. 
* It should be called in the constructor of the Variable class. 
*/ 
void SymbolTable::insert(string variable) 
{ 
    const Symbol& symbol = Symbol(variable, symbolTable.lookUp(variable)); 
    elements.push_back(symbol); 
} 


double SymbolTable::lookUp(string variable) const 
{ 
    for (int i = 0; i < elements.size(); i++) 
     if (elements[i].variable == variable) 
      return elements[i].value; 
     else 
     throw "Error: Uninitialized Variable " + variable; 
    return -1; 
} 

void SymbolTable::init() { 
elements.clear(); // Clears the map, removes all elements. 
} 

variable.h代码：

class Variable: public Operand 
{ 
public: 
    Variable(string name) //constructor 
    { 
     // how do i call symbolTable.insert(name); here 
     // without getting 'symboleTable' was not declared in this scope error 

     this->name = name; 
    } 
    double evaluate(); 
private: 
    string name; 
}; 

variable.cpp代码：

#include <string> 
#include <strstream> 
#include <vector> 
using namespace std; 

#include "expression.h" 
#include "operand.h" 
#include "variable.h" 
#include "symboltable.h" 

extern SymbolTable symbolTable; 

double Variable::evaluate() { 
    return symbolTable.lookUp(name); 
} 

Answer 1

解决办法有两个：

1. 您使用全局变量 - 喜欢你Variable::evaluate()例子。你当然可以在“variable.cpp”中添加你的Variable::Variable()而不是标题。或者你可以把extern SymbolTable symbolTable放到文件“variable.h”中。
2. 你在引用传递到symbolTable到构造函数（也许存储的Variable对象内 - 这样，符号表并不需要是一个全局变量，在所有

顺便说一句，这是通常被认为是不好的风格，在头文件之前添加using namespace std

Answer 2

extern SymbolTable symbolTable;需要进入每个需要symbolTable的人员包含的头文件。然后，在variable.cpp，你需要有SymbolTable symbolTable;

Answer 3

您需要在构造函数中实例化第二个类，这会使其及其成员仅在第一个类的构造函数中可用，或者在全局名称空间。例如：

MyFooClass CFoo; 
MyBarClass CBar; 

MyFooClass::MyFooClass() 
{ 
    CBar = new MyBarClass(); 
    CBar.BarClassMemberFunction(); 
}