Abuse of try and catch in exception handling

I have seen in some real life code that people sometimes use C++ for their convinience. Rather than solving the problem using powerful C++ features, they take dodgy shortcuts. Here is an example of peice of code that shows this abuse with 2 possible solutions.

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
//This example shows how some people abuse throw and catch 

#include<iostream>
using namespace std;
//
//The following interface is defined and being used by many classes
void function1();
//Now some programmer wants to change this to
//int function1();
//But this is not possible since overloading does not work for return types
//
//The same problem could instead be solved by other approach as follows:
void function1(int &abc);
int function1(int dummy1, int dummy2); /*Note 2 dummy to avoid ambiguity with
                    the first overload. If the above overloaded func was not 
                    there then only 1 dummy is sufficient 
*/

int main()
{
  try
  {
    function1();
  }
  catch(int xyz)
  {
    cout<<"\n\n";
    cout<<"The function1() returned "<<xyz<<endl;
    cout<<"\n\n";
  }
  
  int first;
  function1(first);
  cout<<"The 1st overloaded function1() returned "<<first<<endl;
  cout<<"\n\n";

  cout<<"The 2nd overloaded function1() returned "<<function1(3,4)<<endl;
  cout<<"\n\n";

  return 0;
}

void function1()
{
  //function logic
  throw 100;
}

//Overloaded function1()
void function1(int &abc)
{
  abc = 120;
}

//Overloaded function1()
int function1(int dummy1, int dummy2)
{
  return 140;
}

The output is as follows:

Using Const Cast

The following is an example to use the const_cast in C++.

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
//Example shows how to use const_cast
#include<iostream>

using namespace std;

void func1(int *x)
{
  cout<<"\n2. xyz = "<<*x<<endl;

  //Possible but its like cheating
  (*x)++;
}


void func2(const int *x)
{
  cout<<"\n4. xyz = "<<*x<<endl;
  //(*x)++; //Not possible to do this, compile time error
}

int main()
{
  int xyz = 22;
  const int *abc = &xyz;
  cout<<"\n1. xyz = "<<xyz<<endl;
  //func1(abc); //Not possible to call, need a cast, compile time error
  //Use const_cast only when you trust a function to not change the value
  func1(const_cast<int *>(abc)); //Cast the constness of abc away
  cout<<"\n3. xyz = "<<xyz<<endl;
  func2(abc);
  cout<<"\n5. xyz = "<<xyz<<endl;
}

The output of the program is as follows:

Example showing Pass by Value and Pass by Reference

This is a very simple example of Pass by value and pass by reference. I have shown both the simple type and structures in the same example.

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
//Example showing pass by value and pass by reference

#include<iostream>

using namespace std;

//Pass by value
void func1(int num)
{
  num++;
}

//Pass by reference
void func2(int &num)
{
  num++;
}

typedef struct x
{
  int a;
  int *b;
}X ;

//Pass by value, pointer still incremented in b
void newFunc1(X xyz)
{
  xyz.a++;
  (*xyz.b)++;
}

//Pass by reference, both variables incremented
void newFunc2(X &xyz)
{
  xyz.a++;
  (*xyz.b)++;
}

int main()
{
  int someNum = 3;
  cout<<"\n1. someNum = "<<someNum<<endl;
  func1(someNum);
  cout<<"\n2. someNum = "<<someNum<<endl;
  func2(someNum);
  cout<<"\n3. someNum = "<<someNum<<endl;

  cout<<"\n\nTrying this on structures"<<endl;
  X someX;
  someX.a = 13;
  int number = 50;
  someX.b = &number;
  cout<<"\n1. someX.a = "<<someX.a<<"      someX.b = "<<*someX.b<<endl;
  newFunc1(someX);
  cout<<"\n2. someX.a = "<<someX.a<<"      someX.b = "<<*someX.b<<endl;
  newFunc2(someX);
  cout<<"\n3. someX.a = "<<someX.a<<"      someX.b = "<<*someX.b<<endl;
  cout<<endl;
  return 0;
}

The output is as follows:

An example of using Typename with Templates

Typename is used with templates where the type is unknown. Use the keyword typename if you have a qualified name that refers to a type and depends on a template parameter. Only use the keyword typename in template declarations and definitions.

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
//This program shows an how to use typename with templates
//Example from
//http://www.deitel.com/articles/cplusplus_tutorials/20060428/index.html
#include<iostream>

//using namespace std; //No need to use the whole namespace std
using std::cout;
using std::endl;

// function template printArray definition
template<typename T>
void printArray( const T *array, int count )
{
  for ( int i = 0; i < count; i++ )
  {
    cout << array[ i ] << " ";
  }
  cout << endl;
} // end function template printArray

int main()
{
  const int ACOUNT = 5; // size of array a
  const int BCOUNT = 7; // size of array b
  const int CCOUNT = 6; // size of array c

  int a[ ACOUNT ] = { 1, 2, 3, 4, 5 };
  double b[ BCOUNT ] = { 1.1, 2.2, 3.3, 4.4, 5.5, 6.6, 7.7 };
  char c[ CCOUNT ] = "HELLO"; // 6th position for null

  cout << "Array a contains:" << endl;
  // call integer function-template specialization
  printArray( a, ACOUNT );

  cout << "Array b contains:" << endl;
  // call double function-template specialization
  printArray( b, BCOUNT );

  cout << "Array c contains:" << endl;
  // call character function-template specialization
  printArray( c, CCOUNT );

  return 0;
}

Note in the above example you could have replaced 'typename' with 'class' and obtain the same results. Compare this with our basic template example discussed before.

The output of the program is as follows:

Functions, Methods and Operations

In C programming we had functions. In C++ we have functions, methods and operations. Here is what I understand the differences between them are:

• Functions: These are the same old functions used in C programming case
• Methods: OOPS concept used to refer a function inside a class. So if your C++ code has two functions where one of the function is part of a class and the other is directly within the code without being part of a class then the first one is a method and the other one a function.
• Operations: I found operations being used generally in UML based books which may be talking about C++ or Java. As far as I understand, operations are abstract methods. When methods are declared (no implementation) then they are referred to as operations. This is the case when its UML representation like a class diagram or C++ code. When the implementation of that method is done (in C++ code) it i referred to as a method.

A simple example of C++ Exceptions

Exceptions is a very powerful mechanism by which errors can be handled within the programs in C++. In C if an exception occurs (for example overflow, underflow, memory allocation failure, etc) then the program would just crash. In C++ these problems can be handled by use of exceptions.

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
//This example shows different ways of throwing and catching 
//exceptions and handling of exceptions

#include<iostream>
//#include<exception> //May be required on other platforms

using namespace std;

void function1();
void function2();
void function3();
void function4();

class zgException: public exception
{
  //overloading the what() method
  virtual const char* what() const throw()
  {
    return "zgException occured";
  }
} zgEx;


int main()
{
  function1();
  function2();
  function3();
  function4();

  return 0;
}

//Throwing an integer
void function1()
{
  cout<<"\nfunction1()"<<endl;
  try
  {
    throw 123;
  }
  catch(int a)
  {
    cout<<"Exception caught with value "<<a<<endl;
  }
}

//Throwing a string but no mechanism to catch it
void function2()
{
  cout<<"\nfunction2()"<<endl;
  string s = "function2() exception";
  try
  {
    throw s;
  }
  catch(exception &e)
  {
    cout<<"Exception message: "<<e.what()<<endl;
  }
  catch(...)
  {
    cout<<"All exceptions not handled are caught here"<<endl;
  }
}

//Throwing a string and catching it
void function3()
{
  cout<<"\nfunction3()"<<endl;
  string s = "function3() exception";
  try
  {
    throw s;
  }
  catch(exception &e)
  {
    cout<<"Exception message: "<<e.what()<<endl;
  }
  catch (string &ss)
  {
    cout<<"Exception message: "<<ss.c_str()<<endl;
  }
  catch(...)
  {
    cout<<"All exceptions not handled are caught here"<<endl;
  }
}

//Throwing a class and catching it
void function4()
{
  cout<<"\nfunction4()"<<endl;
  string s = "function4() exception";
  try
  {
    throw zgEx;
  }
  catch(exception &e)
  {
    cout<<"Exception message: "<<e.what()<<endl;
  }
  catch(...)
  {
    cout<<"All exceptions not handled are caught here"<<endl;
  }
}

The output is as follows:

A Word and Letter Counter program example

This is a very simple program but people can sometime get lost in writing them. I have not taken into account all the different error scenarios but this program is quite robust.

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
//In this program we will count the total number of words, letters
//and the frequency of each letter. For simplicity we will end the
//program when enter is pressed.
#include<iostream>

using namespace std;

void wordLetterCounter(int &numWords, int &numLetters, int letterCount[]);

int main()
{
  int numWords = 0, numLetters = 0;
  int letterCount[26]={0}; //each letter count init to 0

  cout<<"\n\nPlease enter some words and finish by pressing enter : ";

  wordLetterCounter(numWords, numLetters, letterCount);

  cout<<"\n\nNumber of Words = "<<numWords<<"     Number of Letters = "<<numLetters<<endl;
  cout<<"\nFrequency of letters as follows:"<<endl;
  for(int i = 0; i < 26; i++)
  {
    cout<<char('a'+i)<<" = "<<letterCount[i]<<endl;
  }

  return 0;
}

void wordLetterCounter(int &numWords, int &numLetters, int letterCount[])
{
  char c;
  char lastLetter=' ';

  //Remember 'A'=65, 'Z'=90 and 'a'=97, 'z'=122 in Ascii
  while(cin.get(c))
  {
    //Converting upper to lower case to make it case insensitive
    if(c >= 'A' && c <= 'Z')
      c+=char(32);

    //Increase Letter Count and number of letters
    if(c >= 'a' && c <= 'z')
    {
      letterCount[c - 'a']++;
      numLetters++;
    }

    //Increase number of words
    if(c == ' ' && lastLetter != ' ')
      numWords++;

    //If new line then break;
    if(c == '\n')
    {
      //Before you exit, the numWords should be increased if there was atleast 1 letter
      if(numLetters)
        numWords++;
      break;
    }
    lastLetter = c;
  }
}

The Output is as follows. Note that there is a '.' and many spaces between Dr. and Spock but the wordcount is correct.

An example of C++ Multimap

The following is a simple example of C++ Multimap class.

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
//This program shows use of multi-maps
//We input multiple phone numbers for different people
#include<iostream>
#include<map>
#include <string>

using namespace std;

//forward declaration
void printer(multimap<string, int> pN);

int main()
{
  multimap<string, int> phoneNums;

  //Insert key, value as pairs
  phoneNums.insert(pair<string, int>("Joe",123));
  phoneNums.insert(pair<string, int>("Will",444));
  printer(phoneNums);

  //Insert duplicates
  phoneNums.insert(pair<string, int>("Joe",369));
  phoneNums.insert(pair<string, int>("Smith",567));
  phoneNums.insert(pair<string, int>("Joe",888));
  phoneNums.insert(pair<string, int>("Will",999));
  printer(phoneNums);

  //Checking frequency of different keys
  cout<<"\n\nFrequency of different names"<<endl;
  cout<<"Number of Phones for Joe = "<<phoneNums.count("Joe")<<endl;
  cout<<"Number of Phones for Will = "<<phoneNums.count("Will")<<endl;
  cout<<"Number of Phones for Smith = "<<phoneNums.count("Smith")<<endl;
  cout<<"Number of Phones for Zahid = "<<phoneNums.count("Zahid")<<endl;

  //Print all Joe from the list and then erase them
  pair<multimap<string,int>::iterator, multimap<string,int>::iterator> ii;
  multimap<string, int>::iterator it; //Iterator to be used along with ii
  ii = phoneNums.equal_range("Joe"); //We get the first and last entry in ii;
  cout<<"\n\nPrinting all Joe and then erasing them"<<endl;
  for(it = ii.first; it != ii.second; ++it)
  {
    cout<<"Key = "<<it->first<<"    Value = "<<it->second<<endl;
  }
  phoneNums.erase(ii.first, ii.second);
  printer(phoneNums);

  return 0;
}

//This method prints the vector
void printer(multimap<string, int> pN)
{
  cout<<"\n\nMultimap printer method"<<endl;
  cout<<"Map size = "<<pN.size()<<endl;
  multimap<string, int>::iterator it = pN.begin();
  while(it != pN.end())
  {
    cout<<"Key = "<<it->first<<"    Value = "<<it->second<<endl;
    it++;
  }
}

The output is as follows: