C Tips: How to tell if system is little endian or big endian?

关于不同的字节存储顺序 Little endian 和 Big endian，如果有不清楚的地方请查阅维基百科：http://en.wikipedia.org/wiki/Endianness

C code如下：

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

union TestEndian_Unit
{
	uint16_t value;
	uint8_t bytes[2];
};

/*!
	This function get endianness of current running environment.
	Return value:   0 -- Little endian
	                1 -- Big endian

    Exception 0xFF00 means error occurs.
    
	Reference: http://en.wikipedia.org/wiki/Endianness

	For example:    x86, x86-64 and Windows on PowerPC use little endian;
	                FreeBSD on PowerPC and SPARC use big endian.
*/
int IsBigEndian()
{
	union TestEndian_Unit flag;
	flag.value = 0xFF00;
	if(flag.bytes[0] == 0x00 && flag.bytes[1] == 0xFF)
	{
		return 0;
	}
	else if(flag.bytes[0] == 0xFF && flag.bytes[1] == 0x00)
	{
		return 1;
	}
	else
	{
		fprintf(stderr, "Error occurs in function IsBigEndian().\n");
		exit(0xFF00);
	}
}

如果函数返回0，表示当前系统是Little endian；如果返回1，表示当前系统是Big endian。

参考文献：

• Endianness http://en.wikipedia.org/wiki/Endianness
• Big and Little Endian http://www.cs.umd.edu/class/sum2003/cmsc311/Notes/Data/endian.html