Big endian machine: It thinks the first byte it reads is the biggest.
Little endian machine: It thinks the first byte it reads is the littlest.
#include <stdio.h>
int main(int argc, char **argv)
{
union {
short s;
char c[sizeof(short)];
} un;
un.s = 0x0102;
if (sizeof(short) == 2) {
if (un.c[0] == 1 && un.c[1] == 2)
printf("big-endian\n");
else if (un.c[0] == 2 && un.c[1] == 1)
printf("little-endian\n");
else
printf("unknown\n");
} else
printf("sizeof(short) = %d\n", sizeof(short));
exit(0);
}
总结一下：big endian是适合大家的阅读顺序，little endian则相反。
在/usr/include/中（包括子目录）查找字符串BYTE_ORDER(或_BYTE_ORDER, __BYTE_ORDER)，确定其值。这个值一般在endian.h或machine/endian.h文件中可以找到,有时在feature.h中，不同的操作系统可能有所不同。一般来说，Little Endian系统BYTE_ORDER(或_BYTE_ORDER,__BYTE_ORDER)为1234，Big Endian系统为4321。大部分用户的操作系统（如windows, FreeBsd,Linux）是Little Endian的。少部分，如MAC OS ,是Big Endian 的。本质上说，Little Endian还是Big Endian与操作系统和芯片类型都有关系。
Processor OS Order
x86 (Intel, AMD, … ) All little-endian
DEC Alpha All little-endian
HP-PA NT little-endian
HP-PA UNIX big-endian
SUN SPARC All? big-endian
MIPS NT little-endian
MIPS UNIX big-endian
PowerPC NT little-endian
PowerPC non-NT big-endian
RS/6000 UNIX big-endian
Motorola m68k All big-endian