打包结构与未打包结构：有什么区别？ [英] Packed structs vs. unpacked structs: what's the difference?
问题描述
打包和拆包结构有什么区别？
-
Daniel Rudy
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What is the difference between packed and unpacked structs?
--
Daniel Rudy
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推荐答案
Daniel Rudy写道：
Daniel Rudy wrote:
打包和解包结构有什么区别？
What is the difference between packed and unpacked structs?
如果你有gcc，试试这个 - 在#pragma pack（1）中注释掉/行。
在我的机器/实现上 - 用pragma输出：
sizeof（s1）是10，sizeof（s2）是10
没有pragma：
sizeof（s1）是16，sizeof（s2）是12
足够的信息让你想出来？
#include< stdio.h>
#pragma pack（1）
typedef struct struct_1
{
char a;
int b;
char c;
int d;
} s1;
typedef struct struct_2
{
char a;
char c;
int b;
int d ;
} s2;
int main（无效）
{
printf（" sizeof（s1）是％d，sizeof（s2）是％d \ n，sizeof（s1），sizeof（s2））;
返回0;
}
-
==============
不是一个学生
==============
If you have gcc, try this - comment out/in the #pragma pack(1) line.
On my machine/implementation - with the pragma it outputs:
sizeof(s1) is 10, sizeof(s2) is 10
without the pragma:
sizeof(s1) is 16, sizeof(s2) is 12
Enough info for you to figure it out??
#include <stdio.h>
#pragma pack(1)
typedef struct struct_1
{
char a;
int b;
char c;
int d;
} s1;
typedef struct struct_2
{
char a;
char c;
int b;
int d;
} s2;
int main(void)
{
printf("sizeof(s1) is %d, sizeof(s2) is %d\n", sizeof(s1), sizeof(s2));
return 0;
}
--
==============
Not a pedant
==============
2006-04-09，Daniel Rudy< sp******@spamthis.net>写道：
On 2006-04-09, Daniel Rudy <sp******@spamthis.net> wrote:
打包和解包结构有什么区别？
What is the difference between packed and unpacked structs?
一个是包装好了，另一个可能没包装好。根据我的知识，打包的
关键字会覆盖编译器优化
，这会导致一个或多个数据的自然边界对齐
结构中包含的元素。 包装结构将几乎
总是比其解包的兄弟拥有更小的内存占用。
见这里： http://tinyurl.com/ftv3u
这里就这些问题进行了热烈讨论。
我不知道标准 打包的但这是另一篇在Gnu C环境中解释它的文章：
http://grok2.tripod.com/structure_packing.html
-
Aspirat primo Fortuna labori。
- 维吉尔和所有好老师
One is packed and the other is, probably, not packed. The packed
keyword, to the best of my knowledge, overrides compiler optimisations
which lead to natural boundary alignment of one or more of the data
elements contained in the structure. A "packed" structure will almost
always have a smaller memory footprint than its unpacked brother.
See here: http://tinyurl.com/ftv3u
where there is a typically heated discussion on such issues.
I have no idea on the "standardness" of "packed". but here is another
article explaining it in the Gnu C environment:
http://grok2.tripod.com/structure_packing.html
--
Aspirat primo Fortuna labori.
-- Virgil, and all good teachers
Richard G. Riley写道：
Richard G. Riley wrote:
On 2006-04-09, Daniel Rudy <sp******@spamthis.net> wrote:
打包和解包结构有什么区别？
打包关键字
What is the difference between packed and unpacked structs?
The packed keyword
我不知道标准和标准。 打包。
I have no idea on the "standardness" of "packed".
这不是标准C.
-
pete
It''s not standard C.
--
pete
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