__attribute__((aligned)) type attribute

Usage

You can use the packed and aligned attributes together on the same member to set the alignment to a value. The value is less than the default value, but greater than one.

Example: Alignment of a packed 64-bit unsigned integer

Create alignment.c containing the following code:

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

struct foo {
    uint8_t chA;
    uint64_t dwB __attribute__((packed)) __attribute__((aligned(4)));
};

int main() {
  printf(
      "foo is size %d align %d, with chA at offset %d and dwB at offset %d\n",
      sizeof(struct foo), _Alignof(struct foo), offsetof(struct foo, chA),
      offsetof(struct foo, dwB));
  return 0;
}

Compile alignment.c using the following command:

armclang --target=arm-arm-none-eabi -march=armv7-a alignment.c -o alignment.axf

Run the alignment.axf image. The output is:

foo is size 12 align 4, with chA at offset 0 and dwB at offset 4