What is the usage of macro definition?

A macro definition is a preprocessing directive in the C/C++ languages that is used to replace identifiers in the source code before compilation. It allows you to define a constant, a code snippet, or a function for a given identifier, so that the identifier can be used to represent the defined content in subsequent code.

The basic syntax of macro definitions is as follows:

#define identifier replacement

The identifier is a name made up of letters, numbers, and underscores, and can be replaced with constants, expressions, code snippets, or function calls.

The main uses of macro definitions include:

1. Definition of constants: Macros can be used to replace fixed numerical or string values, making the code easier to read and maintain. For example, #define PI 3.14159.
2. Defining functions: Macros can be used to replace simple function calls, improving code efficiency. For example, #define MAX(x, y) ((x) > (y) ? (x) : (y))
3. Definition of code snippet: Macros can be used to replace repetitive code snippets, improving code reusability and maintainability.
   Example: #define PRINT_INT(x) printf(“%d\n”, x)

It is important to note that macros are simply text replacements, they do not perform type checking or syntax analysis. Therefore, one must be cautious of potential issues when using macros, such as side effects of parameter passing and priority issues. Additionally, macros have a scope that spans the entire source code file, so it is essential to name them carefully to avoid naming conflicts and redefinitions.