I wrote this function for a cache line aligned memory allocator which is for eventual use in my thread pool. It returns the line size (in bytes) of the host machine’s CPU cache, or 0 on failure. You can download it here. The source is below. Feel free to do whatever you want with it.

#ifndef GET_CACHE_LINE_SIZE_H_INCLUDED
#define GET_CACHE_LINE_SIZE_H_INCLUDED
 
// Author: Nick Strupat
// Date: October 29, 2010
// Returns the cache line size (in bytes) of the processor, or 0 on failure
 
#include <stddef.h>
size_t cache_line_size();
 
#if defined(__APPLE__)
 
#include <sys/sysctl.h>
size_t cache_line_size() {
	size_t line_size = 0;
	size_t sizeof_line_size = sizeof(line_size);
	sysctlbyname("hw.cachelinesize", &line_size, &sizeof_line_size, 0, 0);
	return line_size;
}
 
#elif defined(_WIN32)
 
#include <stdlib.h>
#include <windows.h>
size_t cache_line_size() {
	size_t line_size = 0;
	DWORD buffer_size = 0;
	DWORD i = 0;
	SYSTEM_LOGICAL_PROCESSOR_INFORMATION * buffer = 0;
 
	GetLogicalProcessorInformation(0, &buffer_size);
	buffer = (SYSTEM_LOGICAL_PROCESSOR_INFORMATION *)malloc(buffer_size);
	GetLogicalProcessorInformation(&buffer[0], &buffer_size);
 
	for (i = 0; i != buffer_size / sizeof(SYSTEM_LOGICAL_PROCESSOR_INFORMATION); ++i) {
		if (buffer[i].Relationship == RelationCache && buffer[i].Cache.Level == 1) {
			line_size = buffer[i].Cache.LineSize;
			break;
		}
	}
 
	free(buffer);
	return line_size;
}
 
#elif defined(linux)
 
#include <stdio.h>
size_t cache_line_size() {
	FILE * p = 0;
	p = fopen("/sys/devices/system/cpu/cpu0/cache/index0/coherency_line_size", "r");
	unsigned int i = 0;
	if (p) {
		fscanf(p, "%d", &i);
		fclose(p);
	}
	return i;
}
 
#else
#error Unrecognized platform
#endif
 
#endif