Macros and its types in C/C++

A macro is a piece of code in a program that is replaced by the value of the macro. Macro is defined by #define directive. Whenever a micro name is encountered by the compiler, it replaces the name with the definition of the macro. Macro definitions need not be terminated by semi-colon(;).

Below are the program to illustrate the use of macros in C/C++:

Program 1:

C

// C program to illustrate macros 
#include <stdio.h> 
  
// Macro definition 
#define LIMIT 5 
  
// Driver Code 
int main() 
{ 
    // Print the value of macro defined 
    printf("The value of LIMIT"
           " is %d", 
           LIMIT); 
  
    return 0; 
} 

C++

// C++ program to illustrate macros 
#include <iostream> 
using namespace std; 
  
// Macro definition 
#define LIMIT 5 
  
// Driver Code 
int main() 
{ 
    // Print the value of macro defined 
    cout << "The value of LIMIT"
         << " is " << LIMIT; 
  
    return 0; 
} 

Output:

The value of LIMIT is 5

Program 2:

C

// C program to illustrate macros 
#include <stdio.h> 
  
// Macro definition 
#define AREA(l, b) (l * b) 
  
// Driver Code 
int main() 
{ 
    // Given lengths l1 and l2 
    int l1 = 10, l2 = 5, area; 
  
    // Find the area using macros 
    area = AREA(l1, l2); 
  
    // Print the area 
    printf("Area of rectangle"
           " is: %d", 
           area); 
  
    return 0; 
} 

C++

// C++ program to illustrate macros 
#include <iostream> 
using namespace std; 
  
// Macro definition 
#define AREA(l, b) (l * b) 
  
// Driver Code 
int main() 
{ 
    // Given lengths l1 and l2 
    int l1 = 10, l2 = 5, area; 
  
    // Find the area using macros 
    area = AREA(l1, l2); 
  
    // Print the area 
    cout << "Area of rectangle"
         << " is: ", 
        area; 
  
    return 0; 
} 

Output:

Area of rectangle is: 50

Explanation:
From the above program we can see that whenever the compiler finds AREA(l, b) in the program it replaces it with the macros defination i.e., (l*b). The values passed to the macro template AREA(l, b) will also be replaced by the statement (l*b). Therefore, AREA(10, 5) will be equal to 10*5.

Types Of Macros

Object-like Macros: An object-like macro is a simple identifier which will be replaced by a code fragment. It is called object-like because it looks like an object in code that uses it. It is popularly used to replace a symbolic name to numerical/variable represented as constant.

Below is the illustration of a simple macro:

C

// C program to illustrate macros 
#include <stdio.h> 
  
// Macro definition 
#define DATE 31 
  
// Driver Code 
int main() 
{ 
    // Print the message 
    printf("Lockdown will be extended"
           " upto %d-MAY-2020", 
           DATE); 
  
    return 0; 
} 

C++

// C++ program to illustrate macros 
#include <iostream> 
using namespace std; 
  
// Macro definition 
#define DATE 31 
  
// Driver Code 
int main() 
{ 
    // Print the message 
    cout << "Lockdown will be extended"
         << " upto " << DATE 
         << "-MAY-2020"; 
  
    return 0; 
} 

Output:

Lockdown will be extended upto 31-MAY-2020

Chain Macros: Macros inside macros are termed as chain macros. In chain macros first of all parent macro is expand then child macro is expanded.

Below is the illustration of a Chain Macro:

C

// C program to illustrate macros 
#include <stdio.h> 
  
// Macro definition 
#define INSTAGRAM FOLLOWERS 
#define FOLLOWERS 138 
  
// Driver Code 
int main() 
{ 
    // Print the message 
    printf("Geeks for Geeks have %dK"
           " followers on Instagram", 
           INSTAGRAM); 
  
    return 0; 
} 

C++

// C++ program to illustrate macros 
#include <iostream> 
using namespace std; 
  
// Macro definition 
#define INSTAGRAM FOLLOWERS 
#define FOLLOWERS 138 
  
// Driver Code 
int main() 
{ 
    // Print the message 
    cout << "Geeks for Geeks have %dK"
         << " followers on Instagram!"
         << INSTAGRAM; 
  
    return 0; 
} 

Output:

Geeks for Geeks have 138K followers on Instagram!

Explanation:
INSTAGRAM is expanded first to produce FOLLOWERS. Then the expanded macro is expanded to produce the outtcome as 138. This is called the chaining of macros.

Multi-line Macros: An object-like macro could have a multi-line. So to create a multi-line macro you have to use backslash-newline.
Below is the illustration of multiline macros:

C

// C program to illustrate macros 
#include <stdio.h> 
  
// Multi-line Macro definition 
#define ELE 1, \ 
            2, \ 
            3 
  
// Driver Code 
int main() 
{ 
  
    // Array arr[] with elements 
    // defined in macros 
    int arr[] = { ELE }; 
  
    // Print elements 
    printf("Elements of Array are:\n"); 
  
    for (int i = 0; i < 3; i++) { 
        printf("%d  ", arr[i]); 
    } 
    return 0; 
} 

C++

// C++ program to illustrate macros 
#include <iostream> 
using namespace std; 
  
// Multi-line Macro definition 
#define ELE 1, \ 
            2, \ 
            3 
  
// Driver Code 
int main() 
{ 
    // Array arr[] with elements 
    // defined in macros 
    int arr[] = { ELE }; 
  
    // Print elements 
    printf("Elements of Array are:\n"); 
  
    for (int i = 0; i < 3; i++) { 
        cout << arr[i] << ' '; 
    } 
  
    return 0; 
} 

Output:

Elements of Array are:
1  2  3

Function-like Macro: These macros are the same as a function call. It replaces the entire code instead of a function name. Pair of parentheses immediately after the macro name is necessary. If we put a space between the macro name and the parentheses in the macro definition then the macro will not work.
A function-like macro is only lengthened if an only if its name appears with a pair of parentheses after it. If we don’t do this, the function pointer will get the address of the real function and lead to a syntax error.

Below is the illustration of function-like macros:

C

// C program to illustrate macros 
#include <stdio.h> 
  
// Function-like Macro definition 
#define min(a, b) (((a) < (b)) ? (a) : (b)) 
  
// Driver Code 
int main() 
{ 
  
    // Given two number a and b 
    int a = 18; 
    int b = 76; 
  
    printf("Minimum value between"
           " %d and %d is %d\n", 
           a, b, min(a, b)); 
  
    return 0; 
} 

C++

// C++ program to illustrate macros 
#include <iostream> 
using namespace std; 
  
// Function-like Macro definition 
#define min(a, b) (((a) < (b)) ? (a) : (b)) 
  
// Driver Code 
int main() 
{ 
  
    // Given two number a and b 
    int a = 18; 
    int b = 76; 
  
    cout << "Minimum value between"
         << a << " and " << b  
         << " is: " << min(a, b); 
  
    return 0; 
} 

Output:

Minimum value between 18 and 76 is 18

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