# <stdalign.h>

**[<stdalign.h>](https://en.cppreference.com/w/c/header/stdalign)** provides `alignas()` and `alignof()` (C11) for memory alignment control. `alignof(type)` returns its alignment requirement; `alignas(N)` forces a variable or struct member to align to N bytes.

Use it for SIMD operations, hardware register access, or matching binary layouts.

## Example

This example demonstrates alignment queries and enforces 16-byte alignment.

```c
// compile: gcc -std=c11 -o alignexample alignexample.c
// run: ./alignexample
// description: query and enforce memory alignment

#include <stdalign.h>
#include <stdint.h>
#include <stdio.h>

int main() {
    printf("alignof(char) = %zu\n", alignof(char));
    printf("alignof(int) = %zu\n", alignof(int));
    printf("alignof(double) = %zu\n", alignof(double));
    
    alignas(16) float vec[4];
    printf("vec[0] address mod 16 = %zu (should be 0)\n", 
           (uintptr_t)vec % 16);
    
    return 0;
}
```

## Common macros

**Alignment queries**:
- `alignof(type)`: alignment requirement of type (in bytes)

**Alignment enforcement**:
- `alignas(N)`: align variable to N-byte boundary
- `alignas(type)`: align variable same as type

**Usage**:
- `alignas(16) int x;`: align x to 16 bytes
- `alignas(max_align_t) char buf[256];`: align to strictest requirement
- `_Alignas(N)`: C11 keyword form (alignas is macro wrapper)