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 Codeint 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 Codeint main(){ // Print the value of macro defined cout << "The value of LIMIT" << " is " << LIMIT; return 0;} |
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 Codeint 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 Codeint 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;} |
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 Codeint 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 Codeint main(){ // Print the message cout << "Lockdown will be extended" << " upto " << DATE << "-MAY-2020"; return 0;} |
Lockdown will be extended upto 31-MAY-2020
2. 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 Codeint 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 Codeint main(){ // Print the message cout << "Geeks for Geeks have " << INSTAGRAM << "K followers on Instagram!"; return 0;} |
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 Codeint 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 Codeint 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;} |
Elements of Array are: 1 2 3
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 Codeint 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 Codeint 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;} |
Minimum value between 18 and 76 is 18
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