Data Conversion in C++

Difficulty Level : Medium
Last Updated : 18 Nov, 2020

A user-defined data types are designed by the user to suit their requirements, the compiler does not support automatic type conversions for such data types therefore, the user needs to design the conversion routines by themselves if required.

There can be 3 types of situations that may come in the data conversion between incompatible data types:

Conversion of primitive data type to user-defined type: To perform this conversion, the idea is to use the constructor to perform type conversion during the object creation. Below is the example to convert int to user-defined data type:

C++

// C++ program to illustrate the 
// type-conversion 
#include <bits/stdc++.h> 
using namespace std; 
  
// Time Class 
class Time { 
    int hour; 
    int mins; 
  
public: 
    // Default Constructor 
    Time() 
    { 
        hour = 0; 
        mins = 0; 
    } 
  
    // Parameterized Constructor 
    Time(int t) 
    { 
        hour = t / 60; 
        mins = t % 60; 
    } 
  
    // Function to print the value 
    // of class variables 
    void Display() 
    { 
        cout << "Time = " << hour 
             << " hrs and "
             << mins << " mins\n"; 
    } 
}; 
  
// Driver Code 
int main() 
{ 
    // Object of Time class 
    Time T1; 
    int dur = 95; 
  
    // Conversion of int type to 
    // class type 
    T1 = dur; 
    T1.Display(); 
  
    return 0; 
} 

Output:

Time = 1 hrs and 35 mins

Conversion of class object to primitive data type: In this conversion, the from type is a class object and the to type is primitive data type. The normal form of an overloaded casting operator function, also known as a conversion function. Below is the syntax for the same:

operator typename()
{
   // Code
}

Now, this function converts a user-defined data type to a primitive data type. For Example, the operator double() converts a class object to type double, the operator int() converts a class type object to type int, and so on. Below is the program to illustrate the same:

C++

// C++ program to illustrate the 
// above conversion 
#include <bits/stdc++.h> 
using namespace std; 
  
// Tie Class 
class Time { 
    int hrs, mins; 
  
public: 
    // Constructor 
    Time(int, int); 
  
    // Casting operator 
    operator int(); 
  
    // Destructor 
    ~Time() 
    { 
        cout << "Destructor is called."
             << endl; 
    } 
}; 
  
// Function that assigns value to the 
// member variable of the class 
Time::Time(int a, int b) 
{ 
    hrs = a; 
    mins = b; 
} 
  
// int() operator is used for Data 
// conversion of class to primitive 
Time::operator int() 
{ 
    cout << "Conversion of Class"
         << " Type to Primitive Type"
         << endl; 
  
    return (hrs * 60 + mins); 
} 
  
// Function perfomrs type conversion 
// from the Time class type object 
// to int data type 
void TypeConversion(int hour, int mins) 
{ 
    int duration; 
  
    // Create Time Class  object 
    Time t(hour, mins); 
  
    // Conversion OR duration = (int)t 
    duration = t; 
    cout << "Total Minutes are "
         << duration << endl; 
  
    // Conversion from Class type to 
    // Primitive type 
    cout << "2nd method operator"
         << " overloading " << endl; 
  
    duration = t.operator int(); 
  
    cout << "Total Minutes are "
         << duration << endl; 
  
    return; 
} 
  
// Driver Code 
int main() 
{ 
    // Input value 
    int hour, mins; 
    hour = 2; 
    mins = 20; 
  
    // Function call to illustrate 
    // type conversion 
    TypeConversion(hour, mins); 
  
    return 0; 
} 

Output:

Conversion of Class Type to Primitive Type
Total Minutes are 140
2nd method operator overloading 
Conversion of Class Type to Primitive Type
Total Minutes are 140
Destructor is called.

Now, the function will convert the vector to scalar magnitude. The operator double() can be used as:

double len = double(S1);
            Or,
double len = S1;
where S1 is an object of type vector.

Conversion of one class type to another class type: In this type, one class type is converted into another class type. It can be done as follow:

// Objects of different types
objectX = objectY;

See the below example in which we have two classes Time and Minute respectively and will convert one class Time to another Minute class.

C++

// C++ program to illustrate the 
// above conversion 
#include <bits/stdc++.h> 
using namespace std; 
  
// Time Class 
class Time { 
    int hr, mins; 
  
public: 
    // Constructors 
    Time(int h, int m) 
    { 
        hr = h; 
        mins = m; 
    } 
    Time() 
    { 
        cout << "\nTime's Object Created"; 
    } 
    int Minute() 
    { 
        int totalmin = (hr * 60) + mins; 
        return totalmin; 
    } 
  
    // Function to print the value of 
    // hours and minutes 
    void show() 
    { 
        cout << "Hour: " << hr << endl; 
        cout << "Minute : " << mins << endl; 
    } 
}; 
  
// Minutes Class 
class Minute { 
    int mins; 
  
public: 
    // Constructors 
    Minute() 
    { 
        mins = 0; 
    } 
    void operator=(Time T) 
    { 
        mins = T.Minute(); 
    } 
  
    // Function to print the value of 
    // hours and minutes 
    void show() 
    { 
        cout << "\nTotal Minute : " << mins << endl; 
    } 
}; 
  
// Function perfomrs type conversion 
// from the Time class type object 
// to int data type 
void TypeConversion(int hour, int mins) 
{ 
    Time t1(hour, mins); 
    t1.show(); 
    Minute m1; 
    m1.show(); 
  
    // Conversion from Time class 
    // to Minute class 
    m1 = t1; 
    t1.show(); 
    m1.show(); 
} 
  
// Driver Code 
int main() 
{ 
    // Input value 
    int hour, mins; 
    hour = 3, mins = 40; 
  
    // Function Call 
    TypeConversion(hour, mins); 
  
    return 0; 
} 

Output:

Hour: 3
Minute : 40

Total Minute : 0
Hour: 3
Minute : 40

Total Minute : 220

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