Big endian与Little endian的区别

Little endian把低字节存放在内存的低位；而big endian将低字节存放在内存的高位. Intel系列的是采用的little endian的格式存放数据,而motorola系列(powerPPC)的CPU采用的是big endian.

 

为了更好的理解，以下的程序分别运行在x86和ppc的cpu上， 用gdb显示数据的存放方式。

 

#include <stdio.h>

main()
{
   long long a = 0x1122334455667788;
    printf("%lx\n", a);
}


 

1．    X86下的gdb显示

(gdb) p &a

$1 = (long long int *) 0x7fffde588c88

(gdb) x /2x 0x7fffde588c88

0x7fffde588c88: 0x55667788      0x11223344

(gdb) p /x *(char *)0x7fffde588c88  =====è低位地址存放低位数0x88

$3 = 0x88

(gdb) p /x *(char *)0x7fffde588c89

$4 = 0x77

(gdb) p /x *(char *)0x7fffde588c90

$5 = 0x0

(gdb) p /x *(char *)0x7fffde588c8a

$6 = 0x66

(gdb) p /x *(char *)0x7fffde588c8b

$7 = 0x55

(gdb) p /x *(char *)0x7fffde588c8c

$8 = 0x44

(gdb) p /x *(char *)0x7fffde588c8d

$9 = 0x33

(gdb) p /x *(char *)0x7fffde588c8e

$10 = 0x22

(gdb) p /x *(char *)0x7fffde588c8f

$11 = 0x11

 

2．    PPC下的gdb显示

(gdb) p &a

$1 = (long long int *) 0x7ff93af8

 (gdb) p /x *(char *)0x7ff93af8      =========è低位地址存放高位数0x11

$3 = 0x11

(gdb) p /x *(char *)0x7ff93af9

$4 = 0x22

(gdb) p /x *(char *)0x7ff93afa

$5 = 0x33

(gdb) p /x *(char *)0x7ff93afb

$6 = 0x44

(gdb) p /x *(char *)0x7ff93afc

$7 = 0x55

(gdb) p /x *(char *)0x7ff93afd

$8 = 0x66

(gdb) p /x *(char *)0x7ff93afe

$9 = 0x77

(gdb) p /x *(char *)0x7ff93aff

$10 = 0x88

(gdb)