Dado un archivo «Input.txt» en el que cada línea tiene valores iguales a las variables de instancia de una clase.
Lea los valores en el objeto de la clase y realice las operaciones necesarias.
Teoría :
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));
Ejemplos:
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;
}
Producción:
Terry
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Artículo escrito por GeeksforGeeks-1 y traducido por Barcelona Geeks. The original can be accessed here. Licence: CCBY-SA