{"id":111,"date":"2018-07-10T06:27:41","date_gmt":"2018-07-10T06:27:41","guid":{"rendered":"http:\/\/itp1.epgpbooks.inflibnet.ac.in\/?post_type=chapter&p=111"},"modified":"2019-05-14T12:01:23","modified_gmt":"2019-05-14T12:01:23","slug":"the-important-trio","status":"publish","type":"chapter","link":"https:\/\/ebooks.inflibnet.ac.in\/itp1\/chapter\/the-important-trio\/","title":{"rendered":"The Important Trio"},"content":{"raw":"
\"epgp<\/a>\r\n<\/span><\/div>\r\n\r\nIn this module we will discuss about important trio namely\r\n
    \r\n \t
  1. User Defined Destructor<\/li>\r\n \t
  2. User Defined Copy Constructor<\/li>\r\n \t
  3. User Defined Overloaded = Operator<\/li>\r\n<\/ol>\r\nBut before we understand the need of this important trio, let us recall where these functions are used one by one.\r\n\r\n \r\n\r\nDestructors<\/strong>\r\n\r\n \r\n\r\nDestructors are called automatically when object goes out of scope.\r\n\r\nMatrix operator+ (Matrix m)\r\n\r\n{\r\n\r\nMatrix resultant(row,col);\r\n\r\nfor (int i=0; i<row; i++)\r\n\r\nfor (int j=0; j<col; j++)\r\n\r\n \r\n\r\nresultant.matrix[i][j] = matrix[i][j] + m.matrix[i][j]; return resultant;\r\n\r\n}\r\n\r\n \r\n

    As we know the scope of the object is the block in which it is declared and it\u2019s lifetime is the duration for which the block is executing. The Matrix object resultant is declared inside the operator+ function therefore when execution of the function ends the object will go out of scope and destructor will be called for its destruction. Also the formal argument m, which is object of class Matrix will come into existence when control enters function operator+ and will be destroyed once the function ends, by means of invocation of destructor.<\/p>\r\n \r\n\r\nCopy Constructor<\/strong>\r\n\r\n \r\n\r\nCopy Constructor is called:\r\n

      \r\n \t
    1. When we make copy of an object. Time t1(2,30,45);<\/li>\r\n<\/ol>\r\nTime t2(t1);\r\n\r\n \r\n

      Here object t1 is constructed with the help of parameterized constructor initializing its data members namely hrs, minutes and seconds with values 2, 30 and 45 respectively. Object t2 is created as a copy of t1 and its construction is done by copy constructor.<\/p>\r\n\r\n

        \r\n \t
      1. When we pass an object as an argument by value to a method.<\/li>\r\n<\/ol>\r\nMatrix operator+ (Matrix m)\r\n\r\n{\r\n\r\n \r\n\r\nMatrix resultant(row,col); for (int i=0; i<row; i++)\r\n\r\nfor (int j=0; j<col; j++)\r\n\r\nresultant.matrix[i][j] = matrix[i][j] + m.matrix[i][j]; return resultant;\r\n\r\n}\r\n\r\nObjects in C++ are passed by value Here object m will be created as a copy of actual argument and will be constructed by copy constructor.\r\n\r\n \r\n
          \r\n \t
        1. When we return an object from a method by value.<\/li>\r\n<\/ol>\r\n \r\n\r\nMatrix operator+ (Matrix m)\r\n\r\n{\r\n\r\nMatrix resultant(row,col);\r\n\r\n \r\n\r\nfor (int i=0; i<row; i++)\r\n\r\nfor (int j=0; j<col; j++)\r\n\r\n \r\n\r\nresultant.matrix[i][j] = matrix[i][j] + m.matrix[i][j]; return resultant;\r\n\r\n}\r\n\r\n \r\n\r\nAs we know when value is returned from function its temporary copy is created before the returning object goes out of scope and destroyed. This temporary copy is created as copy of returning object using copy constructor.\r\n\r\n \r\n\r\nOverloaded Assignment Operator<\/strong>\r\n\r\n \r\n\r\nOverloaded Assignment Operator is called when one object of the class is assigned to another object of the same class.\r\n\r\n \r\n\r\nvoid main()\r\n\r\n \r\n\r\n{\r\n\r\nMatrix m1(2,2),m2(2,2), result(2,2);\r\n\r\nm1.readMatrix();\r\n\r\nm2.readMatrix();\r\n\r\n \r\n\r\nresult = m1+m2;\r\n\r\ncout << endl << \"The resultant matrix is \" << endl;\r\n\r\nresult.displayMatrix();\r\n\r\n}\r\n\r\n \r\n

          Here in the program the matrix object holding sum of matrix objects m1 and m2 is returned and assigned to matrix object result by means of overloaded assignment operator.<\/p>\r\n \r\n\r\nLet us define the complete Matrix class to understand this.\r\n\r\n \r\n\r\nClass Matrix\r\n\r\n\/* Program : C++ program to add two matrices*\/\r\n\r\n#include<iostream>\r\n\r\n#include<cmath>\r\n\r\nusing namespace std;\r\n\r\nclass Matrix\r\n\r\n{\r\n\r\nint row,col;\r\n\r\nint matrix[10][10];\r\n\r\npublic :\r\n\r\nMatrix()\r\n\r\n{ row = 0; col = 0; } Matrix(int r, int c)\r\n\r\n{\r\n\r\nrow = r; col = c;\r\n\r\nfor (int i=0; i<row; i++) for (int j=0; j<col; j++)\r\n\r\nmatrix[i][j] =0;\r\n\r\n}\r\n\r\nvoid readMatrix()\r\n\r\n{\r\n\r\ncout << endl << \"Enter the matrix\" << endl;\r\n\r\nfor (int i=0; i<row; i++)\r\n\r\nfor (int j=0; j<col; j++)\r\n\r\ncin >> matrix[i][j];\r\n\r\n}\r\n\r\nvoid displayMatrix()\r\n\r\n{\r\n\r\nfor (int i=0; i<row; i++)\r\n\r\n{\r\n\r\nfor (int j=0; j<col; j++)\r\n\r\ncout << matrix[i][j] << \" \";\r\n\r\ncout << endl;\r\n\r\n}\r\n\r\n}\r\n\r\nMatrix operator+ (Matrix m)\r\n\r\n{\r\n\r\nMatrix resultant(row,col);\r\n\r\nfor (int i=0; i<row; i++)\r\n\r\nfor (int j=0; j<col; j++)\r\n\r\nresultant.matrix[i][j] = matrix[i][j] + m.matrix[i][j];\r\n\r\nreturn resultant;\r\n\r\n}\r\n\r\n}; \/\/ end of class\r\n\r\nvoid main()\r\n\r\n{\r\n\r\nMatrix m1(2,2),m2(2,2), result(2,2);\r\n\r\nm1.readMatrix();\r\n\r\n \r\n\r\nm2.readMatrix();\r\n\r\n \r\n\r\nresult = m1+m2;\r\n\r\n \r\n\r\ncout << endl << \"The resultant matrix is \" << endl;\r\n\r\nresult.displayMatrix();\r\n\r\n}\"\"\r\n\r\nIn this program we have not defined destructor or copy constructor or overloaded assignment operator. Then\r\n