Question

MUST BE IN C++

The lab is called "7.3.7.1 Exceptions: file checks"

The lab is as follows:

Objectives

Familiarize the student with:

• situations when exceptions are thrown;
• handling file-related exceptions.

Scenario

Write a class that holds a (2×2) matrix, and add two methods to work with files: one method to load the matrix from a file (in any format) and one method to save the matrix to a file (in the same format). Add code to handle exceptional situations (file not found and no rights to file), print a message and re-throw an exception. Add a try-catch block in the proper places. Simulate both situations handled (try to load a nonexistent file, and try to save a file in a path where you have no proper rights).

Simulate both situations handled

File not found at: path
No rights to write to file: path

Answer 1

#include<iostream>
#include<fstream>
using namespace std;
class matrix //defining a class matrix
{
public:
int a[2][2]; //a 2*2 array
matrix()      //default constructor to initialise each element with 0
{
    a[0][0]=0;
    a[0][1]=0;
    a[1][0]=0;
    a[1][1]=0;
}
void loads(string fName) //function to load data from from file
{
    fstream f;    //an fstream variable
    try     //try block
    {
      f.open(fName, ios::in);//tries opening the file
      if(!f)    //if file not able to open means file not found
        throw 10;   //throws an exception
    }
    catch(int x)    //catches the exception
    {
      cout<<"File not found at: "<<fName;//prints the file not found error
      throw 10;   //re-throw the exception to be caught in main function
    }
    f>>a[0][0]; //if file found then loading data from file
    f>>a[0][1];
    f>>a[1][0];
    f>>a[1][1];
    f.close();    //closing the file
}
void saves(string fName)//saves array in file
{
    fstream f; //an fstream variable
    try
    {
      f.open(fName, ios::out); //opening file in output mode
      if(!f)    //if no right to write the file
        throw 20;   //throw exception
    }
    catch(int x) //catches exception
    {
      cout<<"No rights to write to file: "<<fName; //prints the error
      throw 20;   //re-throws the exception
    }
    f<<a[0][0];//if file has write access the writes to file
    f<<a[0][1];
    f<<a[1][0];
    f<<a[1][1];
    f.close();//closes the file
}
};
int main()
{
matrix m ;//defining a class variable

try
{
    m.loads("example1.txt");//calls loads function
}
catch(int x)//if loads function throws an exception, it is caught by this block
{
    cout<<endl;
}
try
{
    m.saves("example.txt");//calling saves function
}
catch(int x)//if saves function throws an exception, it is caught by this block
{
    cout<<endl;
}
}

INPUT: In file "example.txt"

"example.txt" is made Read-only, so to throw no rights to write in the file.

There is no file named "example1.txt", so to throw exception of file not found.

OUTPUT:

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