# C variadic macros

**C variadic macros** (C99) accept a variable number of arguments using `__VA_ARGS__`. They enable flexible printf-like logging, assertion macros, and generic utilities without separate macro definitions for each argument count.

Use variadic macros for debug logging, flexible error handling, or type-generic operations.

## Example

```c
// compile: gcc -std=c99 -o variadic variadic.c
// run: ./variadic
// description: variadic macros for flexible logging

#include <stdio.h>
#include <stdlib.h>

#define LOG(fmt, ...) \
    do { \
        printf("[LOG] " fmt "\n", __VA_ARGS__); \
    } while(0)

#define ERROR(fmt, ...) \
    do { \
        fprintf(stderr, "[ERROR] " fmt "\n", __VA_ARGS__); \
    } while(0)

#define ASSERT_MSG(cond, fmt, ...) \
    do { \
        if (!(cond)) { \
            fprintf(stderr, "ASSERT FAILED: " fmt "\n", __VA_ARGS__); \
            exit(1); \
        } \
    } while(0)

int main() {
    LOG("Starting program");
    LOG("Value: %d", 42);
    LOG("Name: %s, Age: %d", "Alice", 30);
    
    int x = 10;
    ASSERT_MSG(x > 0, "x must be positive, got %d", x);
    
    printf("Success\n");
    return 0;
}
```

## Common patterns

**`__VA_ARGS__` expansion**:
- Represents all arguments after comma
- Includes any nested commas in arguments

**Empty argument case**:
- Some compilers require at least one arg
- Use `##__VA_ARGS__` to handle empty case (removes trailing comma)

**Debug macros**:
- Combine with `NDEBUG` for conditional compilation
- Printf-style logging without function call overhead

**When to use**:
- Logging and debugging
- Error reporting
- Generic type utilities