無法在文件中寫入數據，程序中沒有錯誤C++

Question

我無法在類中使用這些指針變量寫入數據。程序中沒有錯誤，但沒有數據寫入文件。 請親切地告訴我，我在哪裏做錯了什麼。

#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

，解決了一些點的改寫：

• 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

讓我知道，如果您有任何進一步的問題。

#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

你的構造函數壞了，所有的指針都沒有指定。在分配一個變量之前，您不能使用變量的值。

另外，你使用的是什麼樣的編譯器，或者你有什麼警告設置？您的構造函數正在傳遞指向常量的指針，但它需要非常量指針。那應該肯定已經引起了一個警告，指出你對這些指針的處理不當。

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

請注意，您傳遞構造函數的一堆常量。

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

糟糕，但構造函數需要定期的char*指針。那麼這些指針應該指向什麼呢？

提示：使用明智的C++類，如std::string，這些問題會神奇地消失。