如何在C++中从文件读取/写入文件的类对象（） _fstream

给定文件" Input.txt", 其中每一行的值均与类的实例变量相同。
【如何在C++中从文件读取/写入文件的类对象（）】将值读入类的对象并进行必要的操作。
理论：

The data transfer is usually done using '> > ' and < < ' operators. But if you have a class with 4 data members and want to write all 4 data members from its object directly to a file or vice-versa, we can do that using following syntax :To write object's data members in a file : // Here file_obj is an object of ofstream file_obj.write((char *) & class_obj, sizeof(class_obj)); To read file's data members into an object : // Here file_obj is an object of ifstream file_obj.read((char *) & class_obj, sizeof(class_obj));

例子：

Input : Input.txt : Michael 19 1806 Kemp 24 2114 Terry 21 2400 Operation : Print the name of the highest rated programmer.Output : Terry

C ++

// C++ program to demonstrate read/write of class // objects in C++. #include < iostream> #include < fstream> using namespace std; // Class to define the properties class Contestant { public : // Instance variables string Name; int Age, Ratings; // Function declaration of input() to input info int input(); // Function declaration of output_highest_rated() to // extract info from file Data Base int output_highest_rated(); }; // Function definition of input() to input info int Contestant::input() { // Object to write in file ofstream file_obj; // Opening file in append mode file_obj.open( "Input.txt" , ios::app); // Object of class contestant to input data in file Contestant obj; // Feeding appropriate data in variables string str = "Michael" ; int age = 18, ratings = 2500; // Assigning data into object obj.Name = str; obj.Age = age; obj.Ratings = ratings; // Writing the object's data in file file_obj.write(( char *)& obj, sizeof (obj)); // Feeding appropriate data in variables str = "Terry" ; age = 21; ratings = 3200; // Assigning data into object obj.Name = str; obj.Age = age; obj.Ratings = ratings; // Writing the object's data in file file_obj.write(( char *)& obj, sizeof (obj)); return 0; } // Function definition of output_highest_rated() to // extract info from file Data Base int Contestant::output_highest_rated() { // Object to read from file ifstream file_obj; // Opening file in input mode file_obj.open( "Input.txt" , ios::in); // Object of class contestant to input data in file Contestant obj; // Reading from file into object "obj" file_obj.read(( char *)& obj, sizeof (obj)); // max to store maximum ratings int max = 0; // Highest_rated stores the name of highest rated contestant string Highest_rated; // Checking till we have the feed while (!file_obj.eof()) { // Assigning max ratings if (obj.Ratings > max) { max = obj.Ratings; Highest_rated = obj.Name; } // Checking further file_obj.read(( char *)& obj, sizeof (obj)); } // Output is the highest rated contestant cout < < Highest_rated; return 0; } // Driver code int main() { // Creating object of the class Contestant object; // Inputting the data object.input(); // Extracting the max rated contestant object.output_highest_rated(); return 0; }

输出如下：