c / intermediate
Snippet
Memory Alignment with _Alignas
Certain hardware operations require data to be aligned to specific memory boundaries (e.g., 16-byte boundaries for SIMD instructions). The 'alignas' keyword (from C11) forces the compiler to insert padding to meet these alignment requirements.
snippet.c
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#include <stdio.h>#include <stdalign.h>struct AlignedBuffer {char x;alignas(16) char buffer[16];};int main() {struct AlignedBuffer data;printf("Offset of buffer: %zu\n", (char*)&data.buffer - (char*)&data);return 0;}
Breakdown
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#include <stdalign.h>
Header required for alignment macros like 'alignas'.
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alignas(16) char buffer[16];
Ensures 'buffer' starts at an address that is a multiple of 16.
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(char*)&data.buffer - (char*)&data
Calculates the offset; notice the compiler adds padding after 'x' to align the buffer.