In C Language, a preprocessor is a part of the compiler that processes the source code before actual compilation.
It performs various tasks such as file inclusion, macro expansion, conditional compilation, and other transformations.
The preprocessor directives are commands that are used to control the behaviour of the preprocessor.
Code Reusability: Header files and macros allow us to reuse code across multiple source files, promoting modular and maintainable code.
Debugging and Logging: Macros can be used to define debugging flags or logging functions that are enabled or disabled based on compile-time options.
Performance Optimization: Macros can be used to define inline functions or optimize code for performance, such as loop unrolling or constant folding.
Commonly used preprocessor directives in C programming includes:
#include: The #include directive is used to include header files in the source code. It allows us to reuse code across different source files and external libraries. Header files typically contain declarations and macro definitions needed by our program.
#define: Used to define macros, which are symbolic names representing a code fragment. They provide a way to define reusable pieces of code or constants, allowing for concise and efficient code. Macros are replaced by their corresponding values or code fragments during preprocessing.
#ifdef, #ifndef, #endif: Used for conditional compilation based on expressions allowing parts of the code to be included or excluded based on certain conditions.
#if, #else, #elif: Used for conditional compilation based on expressions allowing parts of the code to be included or excluded based on certain conditions.
#pragma: Used to provide additional information to the compiler, often specific to the compiler being used.
#undef: Used to undefine a previously defined macro.
The preprocessor operates on the source code textually, before any compilation or parsing is done.