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Comprehensive tutorials for advanced C topics: - 15_preprocessor_macros.md (800+ lines) * Complete preprocessor guide * #include, #define, conditional compilation * Header guards, function-like macros * Multi-line macros, stringification, token pasting * Predefined macros, best practices * Extensive Clay examples showing macro patterns - 16_advanced_macros.md (900+ lines) * Variadic macros with __VA_ARGS__ * X-Macros pattern for code generation * _Generic for type-based selection (C11) * Compound literals and statement expressions * For-loop macro trick (Clay's CLAY() macro explained) * Designated initializers in macros * Recursive macro techniques * Complete breakdown of Clay's macro system - 17_memory_management.md (850+ lines) * Stack vs heap memory comparison * malloc, calloc, realloc, free usage * Common memory errors and prevention * Memory leak detection with Valgrind * Arena allocators (Clay's approach) * Memory pools for performance * Memory alignment optimization * Custom allocators * Clay's zero-allocation strategy * Best practices and profiling All files include: - 50+ code examples per chapter - Real Clay library usage throughout - Practice exercises - Performance considerations - Professional patterns Total new content: ~2,500 lines of detailed tutorials
848 lines
17 KiB
Markdown
848 lines
17 KiB
Markdown
# Chapter 16: Advanced Macros and Metaprogramming in C
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## Complete Guide with Clay Library Examples
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---
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## Table of Contents
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1. Variadic Macros
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2. X-Macros Pattern
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3. _Generic for Type Selection (C11)
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4. Compound Literals
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5. Statement Expressions (GCC)
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6. For-Loop Macro Trick
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7. Designated Initializers in Macros
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8. Recursive Macros
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9. Macro Debugging
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10. Clay's Advanced Macro Techniques
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---
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## 16.1 Variadic Macros
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Macros that accept variable number of arguments.
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### Basic Variadic Macro
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```c
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#include <stdio.h>
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#define LOG(format, ...) \
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printf("[LOG] " format "\n", __VA_ARGS__)
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#define ERROR(format, ...) \
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fprintf(stderr, "[ERROR] " format "\n", __VA_ARGS__)
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int main(void) {
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LOG("Program started");
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LOG("Value: %d", 42);
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LOG("X: %d, Y: %d", 10, 20);
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ERROR("File not found: %s", "config.txt");
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return 0;
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}
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```
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**`__VA_ARGS__`** represents all variadic arguments.
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### Empty Variadic Arguments Problem
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```c
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// Problem: No arguments after format
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#define LOG(format, ...) printf(format, __VA_ARGS__)
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LOG("Hello"); // ERROR: too few arguments (missing comma)
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// Solution 1: GCC ##__VA_ARGS__ extension
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#define LOG(format, ...) printf(format, ##__VA_ARGS__)
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LOG("Hello"); // Works
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LOG("Value: %d", 5); // Also works
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// Solution 2: __VA_OPT__ (C++20, C23)
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#define LOG(format, ...) printf(format __VA_OPT__(,) __VA_ARGS__)
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```
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### Named Variadic Arguments
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```c
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#define DEBUG_PRINT(level, format, ...) \
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do { \
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if (debug_level >= level) { \
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printf("[%d] " format "\n", level, __VA_ARGS__); \
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} \
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} while(0)
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int debug_level = 2;
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int main(void) {
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DEBUG_PRINT(1, "Low priority: %s", "message");
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DEBUG_PRINT(3, "High priority: %d", 42);
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return 0;
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}
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```
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### Counting Arguments
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```c
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// Count macro arguments (up to 10)
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#define COUNT_ARGS(...) \
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COUNT_ARGS_IMPL(__VA_ARGS__, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
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#define COUNT_ARGS_IMPL(_1,_2,_3,_4,_5,_6,_7,_8,_9,_10,N,...) N
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int main(void) {
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int count1 = COUNT_ARGS(a); // 1
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int count2 = COUNT_ARGS(a, b, c); // 3
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int count3 = COUNT_ARGS(a, b, c, d, e); // 5
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printf("%d %d %d\n", count1, count2, count3);
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return 0;
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}
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```
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**Clay Example** (from clay.h):
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```c
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// Clay's CLAY() macro uses variadic arguments
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#define CLAY(...) \
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for (CLAY__ELEMENT_DEFINITION_LATCH = ( \
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Clay__OpenElement(), \
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Clay__ConfigureOpenElement(__VA_ARGS__), \
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0 \
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); \
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CLAY__ELEMENT_DEFINITION_LATCH < 1; \
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CLAY__ELEMENT_DEFINITION_LATCH = 1, Clay__CloseElement())
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// Usage with variable configs
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CLAY(CLAY_ID("Button")) { }
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CLAY(CLAY_ID("Box"), CLAY_LAYOUT(.padding = 8)) { }
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CLAY(CLAY_ID("Panel"), CLAY_LAYOUT(...), CLAY_RECTANGLE(...)) { }
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```
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---
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## 16.2 X-Macros Pattern
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Generate code from data tables.
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### Basic X-Macro
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```c
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// Define data once
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#define COLOR_TABLE \
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X(RED, 0xFF0000) \
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X(GREEN, 0x00FF00) \
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X(BLUE, 0x0000FF) \
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X(YELLOW, 0xFFFF00) \
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X(CYAN, 0x00FFFF) \
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X(MAGENTA, 0xFF00FF)
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// Generate enum
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typedef enum {
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#define X(name, value) COLOR_##name,
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COLOR_TABLE
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#undef X
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COLOR_COUNT
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} Color;
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// Generate array of values
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const unsigned int colorValues[] = {
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#define X(name, value) value,
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COLOR_TABLE
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#undef X
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};
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// Generate array of names
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const char* colorNames[] = {
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#define X(name, value) #name,
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COLOR_TABLE
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#undef X
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};
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int main(void) {
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printf("Color: %s = 0x%06X\n",
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colorNames[COLOR_RED],
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colorValues[COLOR_RED]);
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printf("Total colors: %d\n", COLOR_COUNT);
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return 0;
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}
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```
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### Error Code System with X-Macros
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```c
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#define ERROR_CODES \
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X(OK, 0, "Success") \
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X(FILE_NOT_FOUND, 1, "File not found") \
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X(ACCESS_DENIED, 2, "Access denied") \
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X(OUT_OF_MEMORY, 3, "Out of memory") \
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X(INVALID_ARGUMENT, 4, "Invalid argument")
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// Generate enum
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typedef enum {
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#define X(name, code, msg) ERR_##name = code,
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ERROR_CODES
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#undef X
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} ErrorCode;
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// Generate error messages
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const char* getErrorMessage(ErrorCode err) {
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switch (err) {
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#define X(name, code, msg) case ERR_##name: return msg;
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ERROR_CODES
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#undef X
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default: return "Unknown error";
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}
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}
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int main(void) {
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ErrorCode err = ERR_FILE_NOT_FOUND;
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printf("Error %d: %s\n", err, getErrorMessage(err));
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return 0;
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}
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```
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### Clay Example (conceptual):
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```c
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// Clay could use X-macros for element types
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#define CLAY_ELEMENT_TYPES \
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X(RECTANGLE, "Rectangle") \
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X(TEXT, "Text") \
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X(IMAGE, "Image") \
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X(BORDER, "Border") \
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X(CUSTOM, "Custom")
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typedef enum {
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#define X(name, str) CLAY_ELEMENT_TYPE_##name,
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CLAY_ELEMENT_TYPES
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#undef X
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} Clay_ElementType;
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const char* Clay__ElementTypeToString(Clay_ElementType type) {
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switch (type) {
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#define X(name, str) case CLAY_ELEMENT_TYPE_##name: return str;
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CLAY_ELEMENT_TYPES
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#undef X
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default: return "Unknown";
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}
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}
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```
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---
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## 16.3 _Generic for Type Selection (C11)
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Compile-time type-based selection.
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### Basic _Generic
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```c
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#include <stdio.h>
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#define print(x) _Generic((x), \
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int: printf("%d\n", x), \
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float: printf("%.2f\n", x), \
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double: printf("%.4f\n", x), \
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char*: printf("%s\n", x), \
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default: printf("Unknown type\n") \
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)
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int main(void) {
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print(42); // Prints: 42
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print(3.14f); // Prints: 3.14
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print(2.71828); // Prints: 2.7183
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print("Hello"); // Prints: Hello
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return 0;
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}
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```
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### Type-Safe Generic Max
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```c
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#define max(a, b) _Generic((a), \
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int: max_int, \
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long: max_long, \
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float: max_float, \
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double: max_double \
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)(a, b)
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static inline int max_int(int a, int b) {
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return a > b ? a : b;
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}
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static inline long max_long(long a, long b) {
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return a > b ? a : b;
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}
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static inline float max_float(float a, float b) {
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return a > b ? a : b;
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}
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static inline double max_double(double a, double b) {
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return a > b ? a : b;
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}
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int main(void) {
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int i = max(5, 10); // Calls max_int
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float f = max(3.14f, 2.71f); // Calls max_float
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double d = max(1.1, 2.2); // Calls max_double
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printf("%d %.2f %.2f\n", i, f, d);
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return 0;
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}
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```
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### Type Identification
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```c
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#define typename(x) _Generic((x), \
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int: "int", \
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float: "float", \
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double: "double", \
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char: "char", \
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char*: "char*", \
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int*: "int*", \
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default: "unknown" \
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)
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int main(void) {
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int x = 10;
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float y = 3.14f;
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char* str = "hello";
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printf("x is %s\n", typename(x)); // "int"
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printf("y is %s\n", typename(y)); // "float"
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printf("str is %s\n", typename(str)); // "char*"
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return 0;
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}
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```
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---
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## 16.4 Compound Literals
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Create temporary struct/array values.
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### Basic Compound Literals
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```c
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typedef struct {
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int x, y;
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} Point;
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void printPoint(Point p) {
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printf("(%d, %d)\n", p.x, p.y);
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}
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int main(void) {
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// Compound literal
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printPoint((Point){10, 20});
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// Can take address
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Point *p = &(Point){5, 15};
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printf("(%d, %d)\n", p->x, p->y);
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// Array compound literal
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int *arr = (int[]){1, 2, 3, 4, 5};
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printf("%d\n", arr[0]); // 1
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return 0;
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}
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```
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### Compound Literals in Macros
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```c
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#define POINT(x, y) ((Point){x, y})
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#define COLOR(r, g, b, a) ((Color){r, g, b, a})
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typedef struct {
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float r, g, b, a;
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} Color;
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int main(void) {
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Point p1 = POINT(10, 20);
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Color red = COLOR(255, 0, 0, 255);
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return 0;
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}
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```
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**Clay Example** (from clay.h):
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```c
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// Clay uses compound literals extensively
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#define CLAY__INIT(type) (type)
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#define CLAY_COLOR(r, g, b, a) \
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CLAY__INIT(Clay_Color){.r = r, .g = g, .b = b, .a = a}
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#define CLAY_DIMENSIONS(w, h) \
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CLAY__INIT(Clay_Dimensions){.width = w, .height = h}
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// Usage
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Clay_Color red = CLAY_COLOR(255, 0, 0, 255);
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Clay_Dimensions size = CLAY_DIMENSIONS(100, 50);
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```
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---
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## 16.5 Statement Expressions (GCC Extension)
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Create macros that return values safely.
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### Basic Statement Expression
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```c
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#define MAX(a, b) ({ \
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typeof(a) _a = (a); \
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typeof(b) _b = (b); \
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_a > _b ? _a : _b; \
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})
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int main(void) {
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int x = 5, y = 10;
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// Safe: expressions evaluated once
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int max = MAX(x++, y++);
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printf("max=%d, x=%d, y=%d\n", max, x, y);
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// max=10, x=6, y=11 (each incremented once)
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return 0;
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}
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```
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### Complex Statement Expression
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```c
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#define SWAP(a, b) ({ \
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typeof(a) _temp = a; \
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a = b; \
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b = _temp; \
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_temp; \
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})
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int main(void) {
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int x = 10, y = 20;
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int old_x = SWAP(x, y);
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printf("x=%d, y=%d, old_x=%d\n", x, y, old_x);
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// x=20, y=10, old_x=10
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return 0;
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}
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```
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**Note:** Statement expressions are GCC/Clang extension, not standard C.
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---
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## 16.6 For-Loop Macro Trick
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Create scope-based macros with automatic cleanup.
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### Basic For-Loop Trick
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```c
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#define WITH_LOCK(mutex) \
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for (int _i = (lock(mutex), 0); \
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_i < 1; \
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_i++, unlock(mutex))
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// Usage
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WITH_LOCK(&myMutex) {
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// Critical section
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// mutex automatically unlocked when block exits
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}
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```
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### How It Works
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```c
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for (init; condition; increment) {
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body
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}
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// 1. init runs once: lock mutex, set _i = 0
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// 2. condition checked: _i < 1 is true (0 < 1)
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// 3. body executes
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// 4. increment runs: _i++, unlock mutex
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// 5. condition checked: _i < 1 is false (1 < 1)
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// 6. loop exits
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```
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**Clay Example** (from clay.h:2016):
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```c
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// Clay's famous CLAY() macro
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#define CLAY(...) \
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for (CLAY__ELEMENT_DEFINITION_LATCH = ( \
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Clay__OpenElement(), \
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Clay__ConfigureOpenElement(__VA_ARGS__), \
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0 \
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); \
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CLAY__ELEMENT_DEFINITION_LATCH < 1; \
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CLAY__ELEMENT_DEFINITION_LATCH = 1, Clay__CloseElement())
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// Usage: automatically opens and closes elements
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CLAY(CLAY_ID("Button"), CLAY_LAYOUT(...)) {
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CLAY_TEXT(CLAY_STRING("Click me"), ...);
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}
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// Clay__CloseElement() called automatically
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```
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### Step-by-Step Breakdown
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```c
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// This code:
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CLAY(config) {
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// children
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}
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// Expands to:
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for (CLAY__ELEMENT_DEFINITION_LATCH = (
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Clay__OpenElement(), // 1. Open element
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Clay__ConfigureOpenElement(config), // 2. Configure
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0 // 3. Set latch to 0
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);
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CLAY__ELEMENT_DEFINITION_LATCH < 1; // 4. Check: 0 < 1 = true, enter loop
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CLAY__ELEMENT_DEFINITION_LATCH = 1, Clay__CloseElement()) // 7. Set latch=1, close
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{
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// 5. User code runs (children)
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}
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// 6. Back to increment
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// 8. Check condition: 1 < 1 = false, exit loop
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```
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---
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## 16.7 Designated Initializers in Macros
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C99 feature for clean initialization.
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### Basic Designated Initializers
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```c
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typedef struct {
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int x, y, z;
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char *name;
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} Data;
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int main(void) {
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// Order doesn't matter
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Data d = {
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.z = 30,
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.name = "test",
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.x = 10,
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.y = 20
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};
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// Partial initialization (rest = 0/NULL)
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Data d2 = {.x = 5};
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return 0;
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}
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```
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### Macros with Designated Initializers
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```c
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#define CREATE_POINT(x, y) \
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(Point){.x = (x), .y = (y)}
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#define CREATE_COLOR(r, g, b) \
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(Color){.r = (r), .g = (g), .b = (b), .a = 255}
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int main(void) {
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Point p = CREATE_POINT(10, 20);
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Color c = CREATE_COLOR(255, 0, 0);
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return 0;
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}
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```
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|
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**Clay Example** (from clay.h):
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```c
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// Clean API with designated initializers
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#define CLAY_LAYOUT(...) \
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(Clay_LayoutConfig){__VA_ARGS__}
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#define CLAY_SIZING_FIT(min, max) \
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|
(Clay_Sizing){ \
|
|
.type = CLAY_SIZING_TYPE_FIT, \
|
|
.size = {.minMax = {.min = min, .max = max}} \
|
|
}
|
|
|
|
// Usage
|
|
Clay_LayoutConfig layout = CLAY_LAYOUT(
|
|
.sizing = {
|
|
.width = CLAY_SIZING_FIT(100, 500),
|
|
.height = CLAY_SIZING_GROW(0)
|
|
},
|
|
.padding = CLAY_PADDING_ALL(16),
|
|
.childGap = 8
|
|
);
|
|
```
|
|
|
|
---
|
|
|
|
## 16.8 Recursive Macros
|
|
|
|
Macros that appear to call themselves (with limitations).
|
|
|
|
### Deferred Expression
|
|
|
|
```c
|
|
#define EMPTY()
|
|
#define DEFER(x) x EMPTY()
|
|
#define EXPAND(...) __VA_ARGS__
|
|
|
|
#define A() 123
|
|
#define B() A()
|
|
|
|
// Direct expansion
|
|
int x = B(); // Expands to: A()
|
|
|
|
// Deferred expansion
|
|
int y = EXPAND(DEFER(B)()); // Expands to: 123
|
|
```
|
|
|
|
### Recursive List Processing
|
|
|
|
```c
|
|
// Limited recursion using deferred expansion
|
|
#define EVAL(...) EVAL1(EVAL1(EVAL1(__VA_ARGS__)))
|
|
#define EVAL1(...) EVAL2(EVAL2(EVAL2(__VA_ARGS__)))
|
|
#define EVAL2(...) EVAL3(EVAL3(EVAL3(__VA_ARGS__)))
|
|
#define EVAL3(...) EVAL4(EVAL4(EVAL4(__VA_ARGS__)))
|
|
#define EVAL4(...) __VA_ARGS__
|
|
|
|
#define EMPTY()
|
|
#define DEFER(x) x EMPTY()
|
|
#define OBSTRUCT(x) x DEFER(EMPTY)()
|
|
|
|
#define REPEAT(count, macro, ...) \
|
|
REPEAT_IMPL(count, macro, __VA_ARGS__)
|
|
|
|
// Complex implementation...
|
|
```
|
|
|
|
**Note:** True recursion is not possible in standard C preprocessor.
|
|
|
|
---
|
|
|
|
## 16.9 Macro Debugging
|
|
|
|
### Viewing Macro Expansion
|
|
|
|
```bash
|
|
# GCC/Clang: preprocess only
|
|
gcc -E program.c
|
|
gcc -E program.c | grep "main" # Filter output
|
|
|
|
# Save preprocessed output
|
|
gcc -E program.c -o program.i
|
|
|
|
# With line markers
|
|
gcc -E -P program.c # Remove line markers
|
|
```
|
|
|
|
### Debug Macros
|
|
|
|
```c
|
|
// Print macro expansion
|
|
#define SHOW(x) #x
|
|
#define EXPAND_SHOW(x) SHOW(x)
|
|
|
|
#define MY_MACRO(a, b) ((a) + (b))
|
|
|
|
#pragma message "MY_MACRO(1,2) = " EXPAND_SHOW(MY_MACRO(1, 2))
|
|
// Output: MY_MACRO(1,2) = ((1) + (2))
|
|
```
|
|
|
|
### Compile-Time Assertions
|
|
|
|
```c
|
|
// Static assertion
|
|
#define BUILD_BUG_ON(condition) \
|
|
((void)sizeof(char[1 - 2*!!(condition)]))
|
|
|
|
// C11 static_assert
|
|
_Static_assert(sizeof(int) == 4, "int must be 4 bytes");
|
|
```
|
|
|
|
**Clay Example:**
|
|
```c
|
|
// Clay uses assertions for debugging
|
|
#define CLAY__ASSERT(condition) \
|
|
do { \
|
|
if (!(condition)) { \
|
|
Clay__ErrorHandler(...); \
|
|
} \
|
|
} while(0)
|
|
```
|
|
|
|
---
|
|
|
|
## 16.10 Advanced Clay Macro Techniques
|
|
|
|
### Element Configuration
|
|
|
|
```c
|
|
// Multiple configuration macros
|
|
CLAY(
|
|
CLAY_ID("Panel"),
|
|
CLAY_LAYOUT({
|
|
.sizing = {
|
|
.width = CLAY_SIZING_GROW(0),
|
|
.height = CLAY_SIZING_FIXED(200)
|
|
},
|
|
.padding = CLAY_PADDING_ALL(16),
|
|
.childGap = 8
|
|
}),
|
|
CLAY_RECTANGLE_CONFIG({
|
|
.color = CLAY_COLOR(200, 200, 200, 255),
|
|
.cornerRadius = CLAY_CORNER_RADIUS_ALL(8)
|
|
}),
|
|
CLAY_BORDER_CONFIG({
|
|
.width = 2,
|
|
.color = CLAY_COLOR(100, 100, 100, 255)
|
|
})
|
|
) {
|
|
// Children
|
|
}
|
|
```
|
|
|
|
### ID Generation
|
|
|
|
```c
|
|
// String-based IDs
|
|
#define CLAY_ID(label) \
|
|
Clay__HashString(CLAY_STRING(label), 0, 0)
|
|
|
|
// Indexed IDs for lists
|
|
#define CLAY_IDI(label, index) \
|
|
Clay__HashString(CLAY_STRING(label), index, 0)
|
|
|
|
// Usage
|
|
for (int i = 0; i < itemCount; i++) {
|
|
CLAY(CLAY_IDI("ListItem", i)) {
|
|
// Item content
|
|
}
|
|
}
|
|
```
|
|
|
|
### Text Elements
|
|
|
|
```c
|
|
// Macro for text with configuration
|
|
#define CLAY_TEXT(text, config) \
|
|
Clay__OpenTextElement(text, config)
|
|
|
|
// Usage
|
|
CLAY_TEXT(
|
|
CLAY_STRING("Hello World"),
|
|
CLAY_TEXT_CONFIG({
|
|
.fontSize = 24,
|
|
.textColor = CLAY_COLOR(0, 0, 0, 255)
|
|
})
|
|
);
|
|
```
|
|
|
|
---
|
|
|
|
## 16.11 Complete Advanced Example
|
|
|
|
```c
|
|
#define CLAY_IMPLEMENTATION
|
|
#include "clay.h"
|
|
|
|
// Custom button macro
|
|
#define UI_BUTTON(id, text, onClick) \
|
|
CLAY( \
|
|
CLAY_ID(id), \
|
|
CLAY_LAYOUT({ \
|
|
.padding = CLAY_PADDING_ALL(12), \
|
|
.sizing = { \
|
|
.width = CLAY_SIZING_FIT(0, 0) \
|
|
} \
|
|
}), \
|
|
CLAY_RECTANGLE_CONFIG({ \
|
|
.color = CLAY_COLOR(70, 130, 180, 255), \
|
|
.cornerRadius = CLAY_CORNER_RADIUS_ALL(4) \
|
|
}) \
|
|
) { \
|
|
CLAY_TEXT( \
|
|
CLAY_STRING(text), \
|
|
CLAY_TEXT_CONFIG({ \
|
|
.fontSize = 16, \
|
|
.textColor = CLAY_COLOR(255, 255, 255, 255) \
|
|
}) \
|
|
); \
|
|
}
|
|
|
|
// Custom panel macro
|
|
#define UI_PANEL(id, ...) \
|
|
CLAY( \
|
|
CLAY_ID(id), \
|
|
CLAY_LAYOUT({ \
|
|
.padding = CLAY_PADDING_ALL(16), \
|
|
.childGap = 8, \
|
|
.layoutDirection = CLAY_TOP_TO_BOTTOM \
|
|
}), \
|
|
CLAY_RECTANGLE_CONFIG({ \
|
|
.color = CLAY_COLOR(240, 240, 240, 255) \
|
|
}) \
|
|
)
|
|
|
|
int main(void) {
|
|
Clay_BeginLayout();
|
|
|
|
UI_PANEL("MainPanel") {
|
|
CLAY_TEXT(
|
|
CLAY_STRING("Welcome"),
|
|
CLAY_TEXT_CONFIG({.fontSize = 32})
|
|
);
|
|
|
|
UI_BUTTON("SubmitBtn", "Submit", handleSubmit);
|
|
UI_BUTTON("CancelBtn", "Cancel", handleCancel);
|
|
}
|
|
|
|
Clay_RenderCommandArray commands = Clay_EndLayout();
|
|
|
|
return 0;
|
|
}
|
|
```
|
|
|
|
---
|
|
|
|
## 16.12 Key Concepts Learned
|
|
|
|
- ✅ Variadic macros with __VA_ARGS__
|
|
- ✅ X-Macros for code generation
|
|
- ✅ _Generic for type-based selection
|
|
- ✅ Compound literals for temporary values
|
|
- ✅ Statement expressions (GCC)
|
|
- ✅ For-loop macro trick for scope
|
|
- ✅ Designated initializers
|
|
- ✅ Recursive macro techniques
|
|
- ✅ Macro debugging methods
|
|
- ✅ Clay's advanced macro patterns
|
|
|
|
---
|
|
|
|
## Practice Exercises
|
|
|
|
1. Create a logging system with different log levels using variadic macros
|
|
2. Implement a state machine using X-Macros
|
|
3. Build a type-safe print function using _Generic
|
|
4. Design a resource manager with for-loop cleanup macros
|
|
5. Create a unit testing framework using macros
|
|
6. Implement a configurable array type with macros
|
|
7. Build a simple OOP system with macros
|
|
8. Create a domain-specific language using Clay-style macros
|
|
|