无法将数据写入文件，程序C++中没有错误

Question

我无法在类中使用这些指针变量将数据写入文件。程序没有错误，但文件上没有写入数据。 请有人告诉我我做错了什么。

#include <iostream.h>
#include <fstream.h>

class studentinfo
{
    private:/*Creating Private Data Members */
        char* VUID;
        char* campusID;
        char* Studentname;
        char* Fathername;

    public:
        void Storefile();/* Function to Store Data in the File*/
        char Display();/*Function to Read and then Display Data from the File*/
        studentinfo(char*, char*, char*, char*);/*Constructor to initialize Data Members*/
        ~studentinfo();
};

/* Constructor Defined Here*/
studentinfo::studentinfo(char* VUID, char* campusID, char* Studentname, char* Fathername)
{
    cout << "Parameterized Contructor is Called" << endl << endl;
}

/*Destructor Defined Here*/
studentinfo::~studentinfo()
{
    cout << "Destructor Called for destruction of the object" << endl;
    system("pause");
}

/*Function to Store Data in the File Defined here*/
void studentinfo::Storefile()
{
    ofstream re;
    re.open("record.txt");
    if(!re)/*Error Checking Mechanism*/
    {
        cout<<"Error Reading File"<<endl;
    }

    re << VUID << endl << campusID << endl << Studentname << endl << Fathername << endl;/*Using data members to Store data in the File*/
    cout << "All the Data Members are Stored in a File" << endl << endl;
    re.close();
}

/*Function to Read and then Display the data in the File is definde here */              
char studentinfo::Display()
{
    char output[100];/*Array to store and display the data*/
    ifstream reh;
    reh.open("record.txt");
    if(!reh)
    {
        cout << "Error Reading File" << endl;
    }

    cout << "Following is My Data" << endl << endl;
    while(!reh.eof()){
        reh.getline(output, 100, '\n');/*Reading the data and storing it in the 'output' array line by line*/
        cout << output << endl;
    }

    reh.close();
}


/*Main Function starting here*/                  
main()
{
    studentinfo s1("mc130202398", "PMTN08", "Rehan Shahzad Siddiqui","Rizwan Ali Siddiqui");/*Object Created and Initialized by constructor calling*/
    s1.Storefile();/*Function Call*/
    s1.Display();/*Function Call*/

    system("pause");
}

Answer 1

重写，解决了许多问题：

• Removes the need to add using namespace std;
• Uses std::string for the studentinfo member variables as per David Schwartz's recommendation
• Uses a constructor initialisation list to set member variables
• Replaces the unreliable eof() check

如果您还有其他问题，请告诉我。

#include <iostream>
#include <fstream>
#include <string>

class studentinfo
{
    private:/*Creating Private Data Members */
        std::string m_VUID;
        std::string m_campusID;
        std::string m_Studentname;
        std::string m_Fathername;

    public:
        void Storefile();/* Function to Store Data in the File*/
        void Display();/*Function to Read and then Display Data from the File*/
        studentinfo(std::string, std::string, std::string, std::string);/*Constructor to initialize Data Members*/
        ~studentinfo();
};

/* Constructor Defined Here*/
studentinfo::studentinfo(std::string VUID, std::string campusID, std::string Studentname, std::string Fathername)
: m_VUID(VUID)
, m_campusID(campusID)
, m_Studentname(Studentname)
, m_Fathername(Fathername)
{
    std::cout << "Parameterized Contructor is Called" << std::endl << std::endl;
}

/*Destructor Defined Here*/
studentinfo::~studentinfo()
{
    std::cout << "Destructor Called for destruction of the object" << std::endl;
}

/*Function to Store Data in the File Defined here*/
void studentinfo::Storefile()
{
    std::ofstream re;
    re.open("record.txt");
    if(!re)/*Error Checking Mechanism*/
    {
        std::cout << "Error opening file" << std::endl;
    }

    // Using data members to store data in the file
    re << m_VUID.c_str() << std::endl; 
    re << m_campusID.c_str() << std::endl; 
    re << m_Studentname.c_str() << std::endl;
    re << m_Fathername.c_str() << std::endl; 

    std::cout << "All the data members are stored in a file" << std::endl << std::endl;
    re.close();
}

/* Function to read and then display the data in the file is defined here */
void studentinfo::Display()
{
    std::string in;/*Array to store and display the data*/
    std::ifstream reh("record.txt");
    if(!reh)
    {
        std::cout << "Error Reading File" << std::endl;
    }

    std::cout << "Following is My Data" << std::endl << std::endl;
    while(std::getline(reh, in))
    {
        std::cout << in << std::endl;
    }

    reh.close();
}


/* Main Function starts here*/
void main()
{
    // Object created and initialised by calling constructor
    studentinfo s1("mc130202398", "PMTN08", "Rehan Shahzad Siddiqui","Rizwan Ali Siddiqui"); 

    s1.Storefile(); /*Function Call*/
    s1.Display(); /*Function Call*/

    system("pause");
}

Answer 2

您的构造函数已损坏，并且所有指针都未分配。在为变量赋值之前，您不能使用变量的值。

另外，你使用的是什么蹩脚的编译器，或者你有什么警告设置？您的构造函数正在传递指向常量的指针，但它需要非常量指针。这应该肯定引起警告，指出您对这些指针的处理不当。

  studentinfo s1("mc130202398", "PMTN08", "Rehan Shahzad Siddiqui","Rizwan Ali Siddiqui");/*Object Created and Initialized by constructor calling*/

请注意，您向构造函数传递了一堆常量。

studentinfo::studentinfo(char* VUID, char* campusID, char* Studentname, char* Fathername)

糟糕，但构造函数采用常规的char* 指针。那么这些指针应该指向什么？

提示：使用像 std::string 这样合理的 C++ 类，这些问题就会神奇地消失。