Is enum a macro or integer variable in C++?

Question

Is an enum a macro or a variable in C++? I am confused about macros in C++. What is the definition of macro in C++?

Answer 1

Enum

In c++ there are two kinds of enum :

1. enum classes
2. plain enums

This is how to declare them:

enum Day { sunday, monday, tuesday };  // plain enum
enum class Color { red, green, blue }; // enum class

What is the difference?

enums - The enumerator names { sunday, monday, tuesday } are in the same scope as the enum and their values implicitly convert to integers and other types.

enum class - enumerator names { red, green, blue } are local to the enum and their values do not implicitly convert to other types (like another enum or int )

It is generally accepted that enum class is preferred to plain enum because it is part of the c++ type system, they don't convert implicitly to int , they don't pollute the namespace, and they can be forward-declared. Using enum class can protect you from some bugs that can arise form plain enum .

Macro

A macro is a totally different thing. Macros are used by the preprocessor, which is a program that process the source code before compilation. Macros are a piece of code in a program which is given some name. Whenever this name is encountered by the compiler the compiler replaces the name with the actual piece of code. The #define directive is used to define a macro. For example:

#include <iostream> 
  
// macro definition 
#define LIMIT 5 

int main() 
{ 
    for (int i = 0; i < LIMIT; ++i)
    { 
        std::cout << i << "\n"; 
    }  
} 

0
1
2
3
4

A macro can also act like a function

#include <iostream> 
  
// macro with parameter 
#define AREA(l, b) ((l) * (b)) 

int main() 
{ 
    int a = 10, b = 5, area; 
  
    area = AREA(a, b); 
  
    std::cout << "Area of rectangle is: " << area; 
} 

Area of rectangle is: 50

The macro is replaced by the preprocessor so there is no function call. This can make code run faster, however, in c++ functions can be inlined by the compiler which is preferred over using macros. Macros can be problematic if you don't define and use them carefully.