搞不清一个问题。。大虾进!

ianglm

struct struct_size
{
       
        char b;
                int a;
        char c;
       
};
struct_size A;
cout<<sizeof(A); //此处输出结果为12；
struct struct_size
{
         int a;

        char b;
                       char c;
       
};//或把int a 移到int c 的后面，输出结果为：8(编译环境为.net2003)
这是为什么呢？谢谢。。。

此问题已经找到答案。。：http://www.linuxforum.net/forum/ ... mp;o=all&fpart=

[ 本帖最后由 ianglm 于 2006-3-16 10:01 编辑 ]

aldebran

it is related to memory alignment, the purpose of which is to facilate memory access.
variables of int type should be stored in an address which can be divided by 4.
variables of char type have no alignment requirement.

struct {
        char        b;
        int        a;
        char        c;
}
is stored as
        *???        /* b */
        ****        /* a */
        *???        /* c */
here, "*" represents an occupied byte, "?" an unoccupied byte.

struct {
        int        a;
        char        b;
        char        c;
}
is stored as
        ****        /* a */
        **??        /* b c */

net_robber

这个问题是不是在不同编译器上也会有不同结果呢？？？？

westgarden

参《C++程序设计语言》 5.7节中，
关于“对齐”、“空洞”的内容。


另：
蛱jiá
蝴蝶的一类，前足短小，触角锤状，成虫赤黄色，对农作物有害。

pcboyxhy

字节对齐问题

ianglm

原帖由 westgarden 于 2006-3-15 11:49 发表
参《C++程序设计语言》 5.7节中，
关于“对齐”、“空洞”的内容。


另：
蛱jiá
蝴蝶的一类，前足短小，触角锤状，成虫赤黄色，对农作物有害。

不好意思。。把虾和蛱给弄错了。。。看来现在真的要好好的学学语文了：)

ianglm

原帖由 aldebran 于 2006-3-15 11:40 发表
it is related to memory alignment, the purpose of which is to facilate memory access.
variables of int type should be stored in an address which can be divided by 4.
variables of char type have n ...

As what you have told me .I have another question to ask you :

There is another struct:
  sturct struct_size{
   char a;
   char b;
}
what is the result sizeof(struct_size)?

saintdragon

1. 
   
2. There is another struct:
   
3.   sturct struct_size{
   
4.    char a;
   
5.    char b;
   
6. }
   
7. what is the result sizeof(struct_size)?
   

复制代码

结果当然为2

libin1983

原帖由 aldebran 于 2006-3-15 11:40 发表
it is related to memory alignment, the purpose of which is to facilate memory access.
variables of int type should be stored in an address which can be divided by 4.
variables of char type have n ...

有趣
受教！
谢谢

mmx_craft

字节对齐问题啊。 赫赫