Different Between Macros and Functions

In C programming, both macros and functions serve as code snippets that perform specific tasks. However, they have distinct characteristics and usage scenarios. This article aims to provide a clear understanding of the differences between macros and functions in C, highlighting their syntax, behavior, and benefits.

Macros vs. Functions: Overview

Macros and functions are both used to encapsulate code logic, but they differ in several aspects. Here’s an overview of the key differences between macros and functions:

a. Syntax

  • Macros: Defined using the #define directive, macros have a different syntax and don’t require parentheses for arguments.
  • Functions: Defined using a function declaration and definition, functions have a specific syntax with parentheses for arguments.

b. Expansion

  • Macros: Macro invocations are expanded inline during preprocessing, directly substituting the code in the source file.
  • Functions: Function calls are executed during runtime and require a separate function definition.

c. Compilation

  • Macros: Macros are expanded during the preprocessing phase and are not compiled separately.
  • Functions: Functions are compiled separately and can be called from multiple parts of the program.

Parameter Evaluation

Parameter evaluation differs between macros and functions:

a. Macros

  • Eager Evaluation: Macro arguments are not evaluated before substitution, which can lead to unexpected behavior in certain cases.

b. Functions

  • Lazy Evaluation: Function arguments are evaluated before the function call, ensuring predictable behavior.

Performance Considerations

The use of macros and functions can impact program performance:

a. Macros

  • Inline Expansion: Macros are expanded inline, potentially improving performance by eliminating function call overhead.
  • Code Bloat: Macros can lead to code bloat as they are expanded wherever invoked.

b. Functions

  • Modularity: Functions promote modularity and code reuse, as they can be called from multiple parts of the program.
  • Function Call Overhead: Function calls involve overhead due to parameter passing and stack management.

Code Readability and Maintainability

Code readability and maintainability differ between macros and functions:

a. Macros

  • Code Duplication: Macros can lead to code duplication as they are expanded inline wherever invoked.
  • Abbreviated Syntax: Macros may provide shorthand notations but can make code harder to read and understand.

b. Functions

  • Code Reuse: Functions promote code reuse by encapsulating logic that can be called from different parts of the program.
  • Structured Approach: Functions support a structured approach to code organization, enhancing readability and maintainability.


Macros and functions have distinct characteristics and usage scenarios in C programming. Macros provide inline code expansion during preprocessing, while functions offer separate, reusable code blocks executed during runtime. Understanding the differences between macros and functions enables you to choose the appropriate approach based on your program’s requirements. By utilizing macros for code expansion and functions for modular, reusable code, you can write efficient, readable, and maintainable C programs.

Posted in: C