Chapter 18

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Chapter 18

Exception Handling

This activity contains 10 questions.

In your current directory you do not have a file named "foo.txt". What will the following program output?


void main()
{
  ifstream f;
  int num;
  int x=0;

  try {
	  f.open("foo.txt");
	  if (f.fail()) {
		  throw(1);
	  }
	  cout << "The numbers are:" << endl;
	  while (!f.eof()) {
		f >> num;
		cout << num << endl;
	  }
	  f.close();	  
  }
  catch (int x) {
	  cout << "The error is " << x << endl;
  }
}

The error is 0The numbers are:
The error is 1The error is 1The numbers are:
The error is 0

What is the error in the following code?


void main()
{
  ifstream f;
  int num1, num2, val;

  try {
	  f.open("foo.txt");
	  if (f.fail()) {
		  throw(0);
	  }
	  cout << "The numbers are:" << endl;
	  while (!f.eof()) {
		f >> num1;
		f >> num2;
		if (num2==0) {
			throw('x');
		}
		val = num1/num2;
		cout << val << endl;
	  }
	  f.close();	  
  }
  catch (...) {
	  cout << "There was an error." << endl;
  }
  catch (int x) {
	  cout << "The error code is " << x << endl;
  }
}

catch (...) is not allowed. There must be a data type inside the parentheses.Multiple catch statements are not allowed.The catch statements must be listed in order from the most specific first to the most general last.It is not valid to throw('x') because there is no catch statement of type char.

Given the following code, how could we write the function openFile so that it correctly throws an exception if the file does not open correctly?


void main()
{
  ifstream f;
  int num1, num2, val;

  try {
	  openFile(f);
	  cout << "The numbers are:" << endl;
	  while (!f.eof()) {
		f >> num1;
		f >> num2;
		if (num2==0) {
			throw("divide by zero");
		}
		val = num1/num2;
		cout << val << endl;
	  }
	  f.close();	  
  }  
  catch (char *s) {
	  cout << "There was error: " << s << endl;
  }  
}

void openFile(ifstream &f) 
{
   try {
     f.open("fofo.txt");    
     if (f.fail()) {
	  throw("File open failure");
     }
  }
}

void openFile(ifstream &f) 
{
   f.open("foo.txt");    
   if (f.fail()) {
	  throw("File open failure");
   }
}

void openFile(ifstream &f) throws Exception
{
   f.open("foo.txt");    
   if (f.fail()) {
	  throw("File open failure");
   }
}

void openFile(ifstream &f) throw(char *)
{
   f.open("foo.txt");    
   if (f.fail()) {
	  throw("File open failure");
   }
}

You do not have a file named "foo.txt" in the current directory. What will the following program output when run?


void openFile(ifstream &f) throw(char *)
{
    f.open("foo.txt");    
    if (f.fail()) {
	  throw("File open failure");
   }
}

void main()
{
  ifstream f;
  int val;

  openFile(f);
  cout << "The numbers are:" << endl;
  while (!f.eof()) {
	f >> val;
	cout << val << endl;
  }
  f.close();	   
}

File open failureThe program will crash because an exception is thrown but not caught.There will be no output.The numbers are:

In your current directory you have a file named "foo.txt" that contains:

What will the following program output?


void openFile(ifstream &f) throw(char *)
{
	f.open("foo.txt");    
    if (f.fail()) {
	  throw("File open failure");
	}
}

void main()
{
  ifstream f;
  int num1, num2, val;
  int x=1;

  try {
	  openFile(f);
	  cout << "The numbers are:" << endl;
	  while (!f.eof()) {
		f >> num1;
		f >> num2;
		if (num2==0) {
			throw(0);
		}
		val = num1/num2;
		cout << val << endl;
	  }
	  f.close();	  
  }  
  catch (char *s) {
	  cout << "There was error: " << s << endl;
  }  
  catch (int x) {
	  cout << "Divide by zero?  code = " << x << endl;
  }
}

The numbers are:
3
0
Divide by zero? code = 0The numbers are:
Divide by zero? code = 0The numbers are:
3
0The numbers are:
3
Divide by zero? code = 0

Given the following code, what is a valid definition for the openFile function?


// Base class Exception
class Exception
{
public:
	string error;
	Exception();
	Exception(string s);
};

Exception::Exception()
{
	error = "Unknown";
}

Exception::Exception(string s)
{
	error = s;
}

// Class Divide by Zero Exception
class DivideZeroException : public Exception
{
public:
	DivideZeroException(string s);
};

DivideZeroException::DivideZeroException(string s) :
	Exception(s)
{
}


// Class File Exception
class FileException : public Exception
{
public:
	FileException(string s);
};

FileException::FileException(string s) :
	Exception(s)
{
}

void openFile(ifstream &f) throw(FileException)
{		
    f.open("foo.txt");    
    if (f.fail()) {
	  throw(FileException("File open failed"));
    }
}

// Main
void main()
{
  ifstream f;
  int num1, num2, val;
  int x=1;

  try {
	  openFile(f);
	  cout << "The numbers are:" << endl;
	  while (!f.eof()) {
		f >> num1;
		f >> num2;
		if (num2==0)
			throw(DivideZeroException("Divide by zero"));
		}
		val = num1/num2;
		cout << val << endl;
	  }
	  f.close();	  
  }  
  catch (FileException e) {
	  cout << "There was error: " << e.error << endl;
  }  
  catch (DivideZeroException e) {
	  cout << "There was error: " << e.error << endl;
  }
}

void openFile(ifstream &f) throw(...)
{		
    f.open("foo.txt");    
    if (f.fail()) {
	  throw(FileException("File open failed"));
    }
}

void openFile(ifstream f) throw(...)
{		
    f.open("foo.txt");    
    if (f.fail()) {
	  throw(FileException("File open failed"));
    }
}

void openFile(ifstream f) throw(FileException)
{		
    f.open("foo.txt");    
    if (f.fail()) {
	  throw(FileException("File open failed"));
    }
}

void openFile(ifstream &f) throw(FileException)
{		
    f.open("foo.txt");    
    if (f.fail()) {
	  throw(FileException("File open failed"));
    }
}

In your current directory you have a file named "foo.txt" that contains:

What will the following program output?


// Base class Exception
class Exception
{
public:
	string error;
	Exception();
	Exception(string s);
};

Exception::Exception()
{
	error = "Unknown";
}

Exception::Exception(string s)
{
	error = s;
}

// Class Divide by Zero Exception
class DivideZeroException : public Exception
{
public:
	DivideZeroException(string s);
};

DivideZeroException::DivideZeroException(string s) :
	Exception(s)
{
}


// Class File Exception
class FileException : public Exception
{
public:
	FileException(string s);
};

FileException::FileException(string s) :
	Exception(s)
{
}

void openFile(ifstream &f) throw(FileException)
{		
	f.open("foo.txt");    
	if (f.fail()) {
		throw(FileException("File open failed"));
	}
}

// Main
void main()
{
  ifstream f;
  int num1, num2, val;
  int x=1;

  try {
	  openFile(f);
	  cout << "The numbers are:" << endl;
	  while (!f.eof()) {
		f >> num1;
		f >> num2;
		if (num2==0) {
		 throw(
		  DivideZeroException("Divide by zero"));
		}
		val = num1/num2;
		cout << val << endl;
	  }
	  f.close();	  
  }
  catch (Exception e) {
	  cout << "There was error: " << e.error << endl;
  }
}

The numbers are:
3
There was error: Divide by zeroThe numbers are: 3 0 There was error: Divide by zeroThe program will crash because the exceptions thrown are either DivideZeroException or FileException, but only Exception is caught.The numbers are:
3
0

In your current directory you have a file named "foo.txt" that contains:

What will the following program output?


// Base class Exception
class Exception
{
public:
	string error;
	Exception();
	Exception(string s);
};

Exception::Exception()
{
	error = "Unknown";
}

Exception::Exception(string s)
{
	error = s;
}

// Class Divide by Zero Exception
class DivideZeroException : public Exception
{
public:
	DivideZeroException(string s);
};

DivideZeroException::DivideZeroException(string s) :
	Exception(s)
{
}


// Class File Exception
class FileException : public Exception
{
public:
	FileException(string s);
};

FileException::FileException(string s) :
	Exception(s)
{
}

void openFile(ifstream &f) throw(FileException)
{		
	f.open("foo.txt");    
	if (f.fail()) {
		throw(FileException("File open failed"));
	}
}

// Main
void main()
{
  ifstream f;
  int num1, num2, val;
  int x=1;

  try {
	  openFile(f);
	  cout << "The numbers are:" << endl;
	  while (!f.eof()) {
		f >> num1;
		f >> num2;
		if (num2==0) {
		 throw(
		  DivideZeroException("Divide by zero"));
		}
		val = num1/num2;
		cout << val << endl;
	  }
	  f.close();	  
  }
  catch (Exception) {
	  cout << "There was an error." << endl;
  }
  catch (FileException e) {
	  cout << "There was a file error: " << e.error << endl;
  }  
  catch (DivideZeroException e) {
	  cout << "There was a division error: " << e.error << endl;
  } 
}

The numbers are:
3
0
There was a division error: Divide by zeroThe program will not compile because there is no variable in the catch for :

catch (Exception) { The numbers are:
3
There was a division error: Divide by zero The numbers are:
3
There was an error.

If you have already defined a class named "MyClass", which of the following code snippets will throw an exception if there is insufficient memory available to allocate a new node?

It is not possible to determine if insufficient memory is available using try/catch. The only method is to check if p == NULL after the call to new.

MyClass *p;

 try {
	  p = new MyClass();
 }
 catch (MyClass)
 {
	  cout << "Memory error." << endl;
 }

MyClass *p;

 try {
	  p = new MyClass();
 }
 catch (Exception)
 {
	  cout << "Memory error." << endl;
 }

 MyClass *p;

 try {
	  p = new MyClass();
 }
 catch (bad_alloc)
 {
	  cout << "Memory error." << endl;
 }

In your current directory you have a file named "foo.txt" that contains:

What will the following program output?


// Base class Exception
class Exception
{
public:
	string error;
	Exception();
	Exception(string s);
};

Exception::Exception()
{
	error = "Unknown";
}

Exception::Exception(string s)
{
	error = s;
}

// Class Divide by Zero Exception
class DivideZeroException : public Exception
{
public:
	DivideZeroException(string s);
};

DivideZeroException::DivideZeroException(string s) :
	Exception(s)
{
}

// Class File Exception
class FileException : public Exception
{
public:
	FileException(string s);
};

FileException::FileException(string s) :
	Exception(s)
{
}

void openFile(ifstream &f) throw(FileException)
{		
	f.open("foo.txt");    
	if (f.fail()) {
		throw(FileException("File open failed"));
	}
}

// Main
void main()
{
  ifstream f;
  int num1, num2, val;
  int x=1;

  try {
	  openFile(f);
	  cout << "The numbers are:" << endl;
	  while (!f.eof()) {
		f >> num1;
		f >> num2;
		try {
			if (num2==0) {
			 throw(
			  DivideZeroException("Divide by zero"));
			}
			val = num1/num2;
			cout << val << endl;
		}
	    catch (DivideZeroException e) {
			cout << "There was a division error: " 
                             << e.error << endl;
		} 
	  }
	  f.close();	  
  }
  catch (FileException e) {
	  cout << "There was a file error: " << e.error << endl;
  } 
}

The numbers are:
3
There was a division error: Divide by zero
2The numbers are:
3
2
There was a division error: Divide by zeroThe program will not compile; it is not valid to create nested try/catch statements.The numbers are:
3
There was a division error: Divide by zero

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