Question

类BaseSearch是我试图在派生函数（ValueSearch）中调用的基函数。我所讨论的代码特别是在ValueSearch下，调用BaseSearch::Print(line, title).我得到的编译器错误是：我不确定我是否正确使用继承。

Error   1   error C2275: 'std::string' : illegal use of this type as an expression

BaseSearch.cpp

BaseSearch::BaseSearch()
{
}

BaseSearch::~BaseSearch()
{
}

void Print(string line, string title)
{
    char c2 = '_';            //set character to blank value; defines the header row
    char c = '_';             //set character to blank value; defines the searched row
    int numHeader = 0;       //sets the value of character for the header row
    int numLine = 0;         //sets the value of character for the searched row
    c2 = line[numLine];
    while (true)           //force while loop
    {
        c = title[numHeader]; numHeader++;          //header character is set to the title array defined as the entire header string above
        if (c != ',')
        {
            cout << c;                              // couts the header until it reaches a ','
        }
        if (c == ',' || title.size() == numHeader)            // if c reaches a ',' it will print the searched row
        {
            cout << ": ";
            while (line.size() != numLine)
            {
                while (c2 != ',' && line.size() != numLine)
                {
                    cout << line[numLine];
                    numLine++;
                    if (line.size() != numLine)
                        c2 = line[numLine];
                    else
                        break;
                }
                if (line.size() != numLine)
                {
                    numLine++;
                    c2 = line[numLine];
                    cout << "\n";
                    break;
                }
            }

        }

        if (title.size() == numHeader)                            // if c reaches a null value, it breaks until other row is found.
        {
            cout << endl << endl; break;
        }
    }
}

BaseSearch.h

#ifndef BASESEARCH_H
#define BASESEARCH_H
#include <string>

class BaseSearch
{
public:
    BaseSearch();
    virtual ~BaseSearch();  
    virtual void Print(string, string);
};

Value Search.cpp

ValueSearch::ValueSearch()
{
    string input;
}

ValueSearch::~ValueSearch()
{
    //dtor
}

double ValueSearch::getInput()
{
    cout << endl << "Enter the name of the company you would like to search for: ";
    cin >> input;
    return input;
}

void ValueSearch::ValueSearchFunc(int c, int x)
{
    column = c;

    //  cout << "Enter the name of the company you would like to search for: ";
    //  getline(cin, input);
    string line;
    ifstream fs("Stock Database.csv");
    string title;
    getline(fs, title);

    while (!fs.eof())
    {
        getline(fs, line);
        string companyname = "";    //start as blank, then append
        string a;
        int commacount = 0;         //how many commas have we passed
        int ChrCount = 0;               //counter for which character in the line we are looking at

        while (line != "\0")         //while the line does not equal to null value.
        {
            double price;
            price = 0;
            a = line[ChrCount];       //convert char c to a string (a) so that we can append
            ChrCount++;

            if (a == ",")
            {
                commacount++; //increases the comma count as a encounters a comma each time.
            }

            else if (commacount == column && (a != "N" && a != "/" && a != "A")) //if comma count is equal to the set column, it will append the string company name.
            {

                while (a != ",")
                {

                    if (a != ",")
                    {
                        companyname.append(a);
                        a = line[ChrCount];
                        ChrCount++;
                    }
                }ChrCount--;
                price = stod(companyname);
            }

            else if (commacount > column) // if the comma count is any value larger than the column, breaks out of loop.
            {
                break;
            }
            if (input == 0)
            {
                break;
            }
            if (x == 1){
                if (price >= input && price != 0) // if the appended company name is equal to the search input entered, it will cout the entire row.
                    BaseSearch::Print(line, title);
                }
            if (x == 2)
            {
                if (price <= input && price != 0) // if the appended company name is equal to the search input entered, it will cout the entire row.
                    BaseSearch::Print(line, title);
            }//end if

        }
    }
}

ValueSearch.h

#ifndef VALUESEARCH_H
#define VALUESEARCH_H
#include <string>
#include "BaseSearch.h"



class ValueSearch : public BaseSearch
{
public:
    ValueSearch();
    ~ValueSearch();
    double getInput();
    void ValueSearchFunc(int c, int x);
void Print(string,string) {BaseSearch::Print(string,string);}

protected:
private:
    double input;
    int column;
};

#endif

Answer 1

您似乎是C ++的初学者。我将向您展示一个可以成功编译的示例代码。

BaseSearc.h：

#ifndef BASESEARCH_H
#define BASESEARCH_H
#include <string>
using namespace std;

class BaseSearch
{
public:
    BaseSearch();
    ~BaseSearch();  
    void Print(string, string);
};

#endif

BaseSearch.cpp：

#include "BaseSearch.h"
#include <iostream>

BaseSearch::BaseSearch()
{
}

BaseSearch::~BaseSearch()
{
}

void BaseSearch::Print(string line, string title)
{
    cout << "line:" << line << endl;
    cout << "title:" << title << endl;
}

ValueSearch.h：

#ifndef VALUESEARCH_H
#define VALUESEARCH_H
#include <string>
#include "BaseSearch.h"

class ValueSearch : public BaseSearch
{
public:
    ValueSearch();
    ~ValueSearch();
    double getInput();
    void ValueSearchFunc(int c, int x);
protected:
private:
    double input;
    int column;
};

#endif

ValueSearch.cpp：

#include "ValueSearch.h"
ValueSearch::ValueSearch()
{

}

ValueSearch::~ValueSearch()
{

}

double ValueSearch::getInput()
{
    return input;
}

void ValueSearch::ValueSearchFunc(int c, int x)
{
    //where is 'input' from?

    //if (x == 1)
    //{
    //  if (price >= input && price != 0) 
    //      BaseSearch::Print(line, title);
    //}
    //if (x == 2)
    //{
    //  if (price <= input && price != 0) 
    //      BaseSearch::Print(line, title);
    //}//end if

}

但我不知道ValueSearchFunc想要做什么。

Answer 2

代码中没有BaseSearch构造函数/析构函数的实现。 Print函数实现应该是

void BaseSearch::Print(string line, string title)
{
   //code
}

从派生类函数调用基函数？

2 个答案: