What is the complete list and usage scenarios of preprocessor directives in C language?

What is the complete list and usage scenarios of preprocessor directives in C language?

Core Preprocessor Directives:

1. File Inclusion #include

   c
   #include <stdio.h>      // System header
   #include "myheader.h"   // User header
   
   // Conditional inclusion
   #if defined(USE_FEATURE)
   #include "feature.h"
   #endif

2. Macro Definition #define

   c
   // Simple macro
   #define PI 3.14159
   #define MAX_SIZE 100
   
   // Macro with parameters
   #define SQUARE(x) ((x) * (x))
   #define MIN(a, b) ((a) < (b) ? (a) : (b))
   
   // Stringification
   #define STR(x) #x
   #define PRINT_VAR(var) printf(#var " = %d\n", var)
   
   // Token concatenation
   #define CONCAT(a, b) a##b

3. Conditional Compilation

   c
   #if defined(UNIX)
       #include <unistd.h>
   #elif defined(WINDOWS)
       #include <windows.h>
   #else
       #error "Unsupported platform"
   #endif
   
   #ifdef DEBUG
       #define LOG(x) printf x
   #else
       #define LOG(x)
   #endif

4. Error and Warning

   c
   #if SIZE < 0
       #error "Size must be positive"
   #endif
   
   #if !defined(VERSION)
       #warning "VERSION not defined, using default"
       #define VERSION "1.0"
   #endif

5. Line Control #line

   c
   #line 100 "custom.c"
   // Error messages will show as custom.c:100

6. Compiler Directive #pragma

   c
   #pragma once              // Prevent multiple inclusion
   #pragma pack(1)           // Memory alignment
   #pragma warning(disable:4996)  // Disable warning

7. Undefine #undef

   c
   #define TEMP 100
   #undef TEMP

Advanced Usage Scenarios:

1. Cross-platform Compatibility

   c
   #if defined(_WIN32) || defined(_WIN64)
       #define PATH_SEPARATOR '\\'
   #else
       #define PATH_SEPARATOR '/'
   #endif

2. Debug and Logging

   c
   #ifdef DEBUG
       #define DEBUG_PRINT(fmt, ...) printf(fmt, ##__VA_ARGS__)
   #else
       #define DEBUG_PRINT(fmt, ...)
   #endif

3. Version Control

   c
   #define VERSION_MAJOR 2
   #define VERSION_MINOR 5
   #define VERSION_STRING "2.5"

Important Considerations:

• Macros have no type checking
• Macro expansion can cause unexpected side effects
• Prefer const and inline functions over macros