CPP-Module-06

This module is designed to help you understand the different casts in CPP.

Table of Content

• Type Conversion
• Differences and profile of each Cast
• std::numeric_limits
• Static member functions and variables
• What is Serialization and DeSerialization

Type Conversion

In C++, type conversion refers to the process of converting a value from one data type to another.

There are several types of type conversions in C++:

1. Implicit Conversion (Automatic Type Conversion):

int intValue = 5;
float floatValue = intValue; // Implicit conversion from int to float

2. Explicit Conversion (Type Casting):

2.1 - C-Style Casting:

double doubleValue = 3.14;
int intValue = (int)doubleValue; // C-style casting

2.2 - Functional Casting:

double doubleValue = 3.14;
int intValue = int(doubleValue); // Functional casting

3. Static Cast:

The static_cast operator takes an expression as input, and returns the evaluated value converted to the type specified inside the angled brackets.

static_cast is best used to convert one fundamental type into another.

double doubleValue = 3.14;
int intValue = static_cast<int>(doubleValue); // Static cast

The main advantage of static_cast is that it provides compile-time type checking, making it harder to make an inadvertent error.

static_cast is also (intentionally) less powerful than C-style casts, so you can’t inadvertently remove const or do other things you may not have intended to do.

4. Dynamic Cast:

Although dynamic casts have a few different capabilities, by far the most common use for dynamic casting is for converting base-class pointers into derived-class pointers.

This process is called downcasting

class Base {
  // ...
};

class Derived : public Base {
  // ...
};

Base* basePtr = new Derived();
Derived* derivedPtr = dynamic_cast<Derived*>(basePtr); // Dynamic cast

5. Reinterpret Cast:

Converts a pointer type to another pointer type, even if they are not related.

Often used for low-level casting, such as casting between pointers and integers.

Considered unsafe and should be used with caution.

int intValue = 42;
double* doublePtr = reinterpret_cast<double*>(&intValue); // Reinterpret cast

Differences and profile of each cast

Static Cast:

• Used for conversions between related types.
• Resolved at compile-time.
• Generally performs simple conversions, such as widening or narrowing of numeric types.
• Safer than C-style casting but doesn't provide runtime type checking.

double doubleValue = 3.14;
int intValue = static_cast<int>(doubleValue); // Static cast

Dynamic Cast:

• Primarily used in polymorphic class hierarchies (classes with at least one virtual function).
• Performs a runtime check to ensure the conversion is valid.
• Returns a null pointer if the conversion is not possible (when dealing with pointers), or throws a std::bad_cast exception (when dealing with references).
• Provides a safer way to downcast within inheritance hierarchies.

class Base {
  // ...
};

class Derived : public Base {
  // ...
};

Base* basePtr = new Derived();
Derived* derivedPtr = dynamic_cast<Derived*>(basePtr); // Dynamic cast

Const Cast:

• Used to add or remove the const qualifier from a variable.
• Allows modifying a variable that was originally declared as const.
• Should be used with caution to avoid undefined behavior.

const int constValue = 42;
int nonConstValue = const_cast<int>(constValue); // Remove const qualifier

Reinterpret Cast:

• Converts a pointer type to another pointer type, even if they are not related.
• Often used for low-level casting, such as casting between pointers and integers.
• Considered unsafe and should be used with caution.

    int intValue = 42;
    double* doublePtr = reinterpret_cast<double*>(&intValue); // Reinterpret cast

In summary, each type of cast serves a specific purpose:

• Static cast is a general-purpose cast for related types, performed at compile-time.
• Dynamic cast is used for safe downcasting in polymorphic class hierarchies, with runtime type checking.
• Const cast is used to add or remove the const qualifier.
• Reinterpret cast is a low-level cast that is less safe and should be used carefully.

std::numeric_limits

std::numeric_limits is a template class in the C++ Standard Library that provides information about the properties of numeric types.

It is defined in the <limits> header and is part of the <limits> header template library.

The primary purpose of std::numeric_limits is to provide a standardized way to obtain information about the characteristics of numeric types, such as the minimum and maximum representable values, whether the type is signed or unsigned, and other properties.

Here are some common members of std::numeric_limits:

• min() and max(): These functions return the minimum and maximum finite representable values of a numeric type.

• lowest(): This function returns the most negative finite representable value for a floating-point type.

• is_integer: A boolean value indicating whether the type is an integer type (true for integer types, false for floating-point types).

• is_signed: A boolean value indicating whether the type is signed (true for signed types, false for unsigned types).

• digits and digits10: These members indicate the number of binary digits (bits) and decimal digits that can be represented exactly in the given numeric type.

• epsilon(): Returns the difference between 1 and the smallest value greater than 1 that is representable for the given floating-point type.

• infinity() and quiet_NaN(): Return positive infinity and a quiet NaN (Not a Number) for floating-point types.

Here's a simple example demonstrating the use of std::numeric_limits:

#include <iostream>
#include <limits>

int main() {
    std::cout << "Minimum value for int: " << std::numeric_limits<int>::min() << std::endl;
    std::cout << "Maximum value for int: " << std::numeric_limits<int>::max() << std::endl;
    std::cout << "Is int signed? " << std::numeric_limits<int>::is_signed << std::endl;

    std::cout << "Minimum value for float: " << std::numeric_limits<float>::min() << std::endl;
    std::cout << "Maximum value for float: " << std::numeric_limits<float>::max() << std::endl;

    return 0;
}

This program prints information about the minimum and maximum values and signedness of int and float types using std::numeric_limits.

Static member functions

Static member functions in C++ are class-level functions that are associated with the class itself rather than with individual instances (objects) of the class.

They are declared using the static keyword, and we can call such a function with a class name without the need to create an object.

Static member functions are commonly used for operations that are related to the class as a whole rather than to specific instances.

Syntax:

The syntax for defining a static member function in C++ is as follows:

    class ClassName
    {
        public:
            static returnType functionName(parameters)
            {
                 // Function body implementation
            }
    };

Static member variables

Before we go into the static keyword as applied to member variables, first consider the following class:

#include <iostream>

struct Something
{
    int value{ 1 };
};

int main()
{
    Something first{};
    Something second{};

    first.value = 2;

    std::cout << first.value << '\n';
    std::cout << second.value << '\n';

    return 0;
}

• When we instantiate a class object, each object gets its own copy of all normal member variables.

• In this case, because we have declared two Something class objects, we end up with two copies of value: first.value, and second.value. first.value is distinct from second.value. Consequently, the program above prints:

2
1

Member variables of a class can be made static by using the static keyword.

Unlike normal member variables, static member variables are shared by all objects of the class. Consider the following program, similar to the above:

#include <iostream>

struct Something
{
    static int s_value; // now static
};

int Something::s_value{ 1 }; // initialize s_value to 1

int main()
{
    Something first{};
    Something second{};

    first.s_value = 2;

    std::cout << first.s_value << '\n';
    std::cout << second.s_value << '\n';
    return 0;
}

This program produces the following output:

2
2

Because s_value is a static member variable, s_value is shared between all objects of the class.

Consequently, first.s_value is the same variable as second.s_value. The above program shows that the value we set using first can be accessed using second!

What is serialization and deserialization

Serialization is a technique for converting an item into a byte sequence that may be kept in memory. Once produced, the byte stream can be streamed to a remote receiving end through a communication channel. Deserialization is the inverse of serialization.

Once produced, the deserliazation process byte stream converts into the original object definition. The C++ runtimes used this method to transfer compiled memory structures through the different components of application dynamic runtimes.