OOP in C++

Suggested Coding Standard

The following is a suggested coding standard/style. It is important to follow a standard when developing code in order to be consistent, readable and maintainable. Hopefully you will apply this or some thing better than this in your software development practice.

· Write only one class per .h and .cpp file

· For each class that you write, in the top of the .h file write a paragraph explaining the purpose of the class

· For each function/method that you write in the class, right below the declaration of the method, write a few lines explaining the purpose of the function and the nature/requirement of the input arguments and the result(s)

· In the .cpp file, write a few lines of comments where ever you do some thing that is a little bit more complicated, or not very obvious.

· Write your variable names so that they are readable and meaningful. For instance, instead of i, t, val, tem, etc. use words that mean something in your program, use names that relate to some logic in your business logic, like initialTemperature, temperature, etc.

· Use mixed case for class names, example, BankAccount instead of Bankaccount

· Begin class names with an upper case letter, Bank instead of bank. If using the C in front of class name (like most Microsoft’s classes), make the second letter caps as well, CBank instead of Cbank.

· Begin all variables and methods with lower case letters (methods in MFC begin with upper case letters, I like to begin with lower case, but what ever you use, be consistent with your own code). Use mixed case. If your variable name or method name has multiple words, use upper case for first letter of each word. Examples:

int temperature;

bool switchStatus;

double upperLimit;

If you use hungarian notation, then the variable names begin with upper case after the m_typePrefix. Again, be consistent with your style.

void closeWindow();

void takeUmbrella();

· You may use hungarian notation for variable names (see below for details)

· Make all member variables private unless you have a very justifiable reason

· Make helper methods private

· Use proper indentation in your code. For example:

if (raining)

{

lockCarWindow();

takeUmbrella();

}

· Use as much free space and extra lines as you can to make the code more readable:

if(value<0) { return noWay; } else{ okToDeposit = true;}

proceedWithDeposit();

You may write the same code as follows:

if (value < 0)

{

return noWay;

}

else

{

okToDeposit = true;

}

proceedWithDeposit();

Commenting:

· In the header file (.h) write a few lines (4-5) describing the class.

· For each function (in .h file) write

· one line describing the purpose of that function.

· one line describing the input requirements and required state of the object

· one line describing the output and resulting state of the object

· one line with a list of exceptions being thrown

· For each function (in .cc file) write comments where ever necessary describing

some things that are special or that may not be obvious to the general reader.

Hungarian Notation (This notation has fallen out of flavor. Some people use m_varname ignoring the type):

MSVC++ uses the Hungarian Notation by Charles Simonyi of Microsoft. In this convention, variable names are prefixed with type information.

The common prefixes are given below:

Prefix Type

i int

n short

u unsigned

b boolean

l long

f float

d double

c char

s char array, string

p pointer

m_ member variable

g_ global variable

Example:

int m_iCount; // member variable Count of integer type

double g_dPressure; // Pressure is a global variable, of type double

CAccount* m_pAccount; // a member variable that is a pointer to Account.

//An example that uses these conventions:

/************************************************************/

// File: Account.h

/*

The purpose of the CAccount class is to abstract a simple Bank Account. It provides functions to deposit money, withdraw money and obtain the balance information. It takes care of making sure that the balance does not drop below 0. Any thing else that you want to convey to the developer not familiar with your code (this may be yourself after a vacation or holiday!). */

class CAccount {

public:

CAccount(double initialBalance);

void withdraw(double amount);

// Purpose: To withdraw money from the account.

// Requirement: current balance > 0

// Promise: Reduces the balance by the said amount, provided the

// amount is less than the current balance.

// Exception: Throws CAccount::InsufficientFund if balance < amount.

void deposit(double amount);

// Purpose: To deposit money into the account.

// Requirement: -

// Promise: Increases the balance by the given amount.

// Exception: Throws CAccount::InvalidAmount if amount < 0.

double getBalance() const;

// Purpose: Returns the balance of the account.

// Requirement: -

// Promise: -

// Exception: -

// The InsufficientFund is an exception class that indicates the condition when the balance is

// too low to perform some transactions.

class InsufficientFund {};

// The InvalidAmount is an exception class...

class InvalidAmount{};

private:

double m_dBalance;

};

/************************************************************/

//File: Account.cpp

#include <Account.h>

CAccount::CAccount(double initialBalance)

{

m_dBalance = initialBalance;

}

void withdraw(double amount)

{

if (m_dBalance < amount)

{

throw InsufficientFund();

}

m_dBalance -= amount;

}

void deposit(double amount)

{

// Let us check the unlikely situation when amount is

// negative

if (amount < 0)

{

throw InvalidAmount();

}

m_dBalance += amount;

}