结构体 [英] structure

问题描述

亲爱的所有人!!


在我开始讨价还价之前，我想问一下我的分析和我的

知识

结构a {

int raw;

char数据;

};


上面结构的大小是8字节...正确（我说的是

32位处理器）


结构a {

int raw;

char data_1;

char data_2;

};


再次上面结构的大小是8个字节。


意味着填充的结构正在进行......正确...


现在假设我必须按顺序分配4位，

然后我要做的是


strcut a {


cahr a：4;

}


现在理想情况下我应该得到上面结构的大小

4比特，但实际上我将获得1个字节，再次我运行的情况

，我不想分配额外的4位（默认情况下

struc ture正在填充），


现在我的问题来了。


首先

我将如何分配仅4位，


秒（不直接与上面相关）

我将如何保证结构与机器长度对齐？

我必须在结构中做些什么才能确保它是

分配到机器字长度。


我支持使用Strcuture填充来快速完成艺术表演....... mi正确，因为它与机器长度相符

。

请让我知道上面的querry


在此先感谢

Ranjeet

Dear All !!

Before i qoute my querry, I will like to qoute my analysis and my
Knowledge

Struct a {
int raw;
char data;
};

the size of above struct is 8 byte ... correct (I am talking of
32 bit procesor)

Struct a {
int raw;
char data_1;
char data_2;
};

again the size of above structure is 8 bytes.

Means the structure of padding is going on... right...

Now suppose I have to specefically allocate the 4 bits,
then What i will do is

strcut a {

cahr a:4;
}

now ideally speaking i should get the size of the above struct as
4 bits, But infact i will get the 1 byte, Again i run in the situation
that i dont want to allocate the extra 4 bits (which by default
structure is doing padding),

now my question comes.

First
how I am going to allocate the 4 bits only,

second (not directly realated to the above)
how i will assure that structure is alligned to the machine lenght ?
what i have to do in the structure that make me sure that it is
alligned to the machine word lenght.

I supposse that Strcuture padding is done to get the exectution of
Arthematic execution fast.... m i correct as it is alligned
to the machine length.

Please let me know about the above querry

Thanks In Advance
Ranjeet

推荐答案

1。通过说，


char a：4;


你不只是分配4位，相反，你要求

用于逐位分配。假设，你知道你有三个

属性，已知范围，你可以说，


struct bitwise_alloc

{

char a：4; （范围0到15）

char b：2; （范围0到3）

char c：1; （范围0到1）

char d：1;

};


大小仍然是1个字节（如果填充不存在）。没有分配

低于1个字节是可能的（对于一个对象/变量）。


2.你可以使用编译器指令（#pragma pack）来做到这一点，

但是它可能不是一般的实现。

1. by saying,

char a:4;

you are not just allocating 4 bits, instead, you are requesting
for a bit-wise allocation. Suppose, you know that you have three
attributes, with known ranges, you could say,

struct bitwise_alloc
{
char a:4; (range 0 to 15)
char b:2; (range 0 to 3)
char c:1; (range 0 to 1)
char d:1;
};

The size would still be 1 byte (if padding is not there). No allocation
below 1 byte is possible (for an object/variable).

2. you could do this using the compiler directive (#pragma pack),
but then it might not be a generic implementation.

ra *********** @ gmail.com 写道：

亲爱的所有人!!

在我讨论我的问题之前，我想问一下我的分析和我的知识

结构{
int raw ;
char数据;
};

上面结构的大小是8字节...正确（我说的是32位处理器）

结构一个{
int raw;
char data_1;
char data_2;
};

再次上面结构的大小是8个字节。

意味着填充的结构正在进行......正确...

现在假设我必须按顺序分配4位，
然后我是什么将要做的是

strcut a {

cahr a：4;
}
位域适用于* int * s
我不想分配额外的4 bits（默认情况下
结构正在填充），


您可以获得结构的大小（实际上是任何数据类型或变量）

至少是字节的倍数。

现在我的问题来了。

首先
我将如何分配4位，
我认为，分配4位内存是不可能的。但是你可以指定__attribute __（（__ packed__））以及结构定义来

打包到字节对齐的分配。

second（不是直接的）如上所述）
我将如何确保结构与机器长度相对应？
我必须在结构中做些什么才能确保它与机器字对齐lenght。


__attribute __（（__ align__））可能对你有帮助。


-

Mohan

我认为Strcuture填充是为了快速实现Arthematic执行的执行.... mi正确，因为它与机器长度相对应。

请让我知道上面的问题

在此先感谢
Ranjeet

Dear All !!

Before i qoute my querry, I will like to qoute my analysis and my
Knowledge

Struct a {
int raw;
char data;
};

the size of above struct is 8 byte ... correct (I am talking of
32 bit procesor)

Struct a {
int raw;
char data_1;
char data_2;
};

again the size of above structure is 8 bytes.

Means the structure of padding is going on... right...

Now suppose I have to specefically allocate the 4 bits,
then What i will do is

strcut a {

cahr a:4;
} bitfield are appropriate for *int*s

now ideally speaking i should get the size of the above struct as
4 bits, But infact i will get the 1 byte, Again i run in the situation
that i dont want to allocate the extra 4 bits (which by default
structure is doing padding),
You can get size of a structure (infact any data type or variable)
atleast in multiples of byte.


now my question comes.

First
how I am going to allocate the 4 bits only, I think, allocating a memory of 4bits is not possible. However you can
specify __attribute__((__packed__)) along with structure definition to
pack the allocation to byte aligned.

second (not directly realated to the above)
how i will assure that structure is alligned to the machine lenght ?
what i have to do in the structure that make me sure that it is
alligned to the machine word lenght.
__attribute__ ((__aligned__)) might help you.

--
Mohan

I supposse that Strcuture padding is done to get the exectution of
Arthematic execution fast.... m i correct as it is alligned
to the machine length.

Please let me know about the above querry

Thanks In Advance
Ranjeet

Mukul Pandey写道：

Mukul Pandey wrote:

1.通过说，

char a：4;

你不仅仅是相反，分配4位，您要求进行逐位分配。假设，你知道你有三个
属性，已知范围，你可以说，

struct bitwise_alloc
{
char a：4; （范围0到15）
char b：2; （范围0到3）
char c：1; （范围0到1）
char d：1;
};

大小仍然是1个字节（如果没有填充）。没有分配
低于1个字节是可能的（对于一个对象/变量）。


是的，你说的是对的。

2.你可以使用编译器指令（#pragma pack）来做到这一点，
但是然后它可能不是一般的实现。

1. by saying,

char a:4;

you are not just allocating 4 bits, instead, you are requesting
for a bit-wise allocation. Suppose, you know that you have three
attributes, with known ranges, you could say,

struct bitwise_alloc
{
char a:4; (range 0 to 15)
char b:2; (range 0 to 3)
char c:1; (range 0 to 1)
char d:1;
};

The size would still be 1 byte (if padding is not there). No allocation
below 1 byte is possible (for an object/variable).
yes you are correct what you are saying.

2. you could do this using the compiler directive (#pragma pack),
but then it might not be a generic implementation.

如果你给我一些指针，这对我有帮助

（任何网站链接/ Pseduo代码）

It will be help me if you give me some pointer on this
(Any web link / Pseduo code)

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