wtf是这个？ [英] wtf is this?
问题描述
这是我第一次看到这样的代码而且我不知道这意味着什么
。它似乎是C代码，但我认为我很熟悉
大多数构造......一定是错过了一个：
u_char c_perm：3;
这个声明是在一个结构内部以及以类似方式声明的其他几个
变量。
我是假设u_char是unsigned char的typedef，但是什么是
" ：3部分在那里做什么，这是什么意思？这是来自
C99的新语法还是一直存在，我以前从未碰到过它？
我在Xok exokernel中找到了这段代码麻省理工学院如果它产生差异或
你很好奇。
谢谢，
NR
This is the first time I have seen code like this and I don''t know what
it means. It appears to be C code but I thought I was familiar with
most constructs...must have missed one:
u_char c_perm : 3;
This declairation is inside of a struct along with several other
variables declaired in a similar manner.
I am assuming u_char to be a typedef for unsigned char, but what is the
" : 3" part doing there and what does it mean? Is this new syntax from
C99 or has it always been around and I just never ran into it before?
I found this code in the Xok exokernel from MIT if it makes a diff or
you are curious.
Thanks,
NR
推荐答案
Noah Roberts写道：
Noah Roberts wrote:
这是我第一次看到这样的代码，我不知道是什么这意味着。它似乎是C代码，但我认为我熟悉大多数构造......一定是错过了一个：
u_char c_perm：3;
This is the first time I have seen code like this and I don''t know what
it means. It appears to be C code but I thought I was familiar with
most constructs...must have missed one:
u_char c_perm : 3;
你不要问，直到你确定你找不到答案然后你会这样做：你真的知道这是什么我只是没见过它
使用了所以忘了它。我从来没有真正看到使用
位域的代码，这并不是唯一奇怪的事情：
/ *七个数组（7 - I ''作弊）字节命名能力如果
*它不是指针：* /
u_char c_name [1];
/ *如果这是一个指针，能力列表的长度和地址：* /
u_short cl_len;
struct Capability * cl_list;
当然这段代码并不是完全可移植的：P
NR
You hold off asking until you are sure you can''t find the answer and
then you do :P I actually knew what this was I just hadn''t ever seen it
used so forgot all about it. I have never actually seen code that used
bitfields, and that isn''t the only strange thing it does:
/* An array of seven (7--I''m cheating) bytes naming the capability if
* it is not a pointer: */
u_char c_name[1];
/* The length and address of the capability list if this is a pointer: */
u_short cl_len;
struct Capability *cl_list;
Of course this code is not meant to be exactly portable :P
NR
" Noah Roberts < NR ****** @ dontemailme.com>在消息中写道
news：bl ********** @ quark.scn.rain.com ...
"Noah Roberts" <nr******@dontemailme.com> wrote in message
news:bl**********@quark.scn.rain.com...
Noah Roberts写道：
Noah Roberts wrote:
这是我第一次看到这样的代码而且我不知道它意味着什么。它似乎是C代码，但我认为我很熟悉
大多数构造......一定是错过了一个：
u_char c_perm：3;
你推迟询问直到你肯定你找不到答案然后你会这样做：PI实际上知道这是什么我只是没见过>
This is the first time I have seen code like this and I don''t know what
it means. It appears to be C code but I thought I was familiar with
most constructs...must have missed one:
u_char c_perm : 3;
You hold off asking until you are sure you can''t find the answer and
then you do :P I actually knew what this was I just hadn''t ever seen it >
使用所以忘记了一切。我从来没有真正看到使用过bitfields的代码，这并不是唯一奇怪的事情：
你觉得奇怪的是什么？
/ *七个（7个我作弊）字节的数组命名能力，如果
*它不是一个指针：* /
u_char c_name [1];
这是*一个*类型''u_char''对象的数组。
/ *能力列表的长度和地址，如果这个是一个指针：* /
u_short cl_len;
struct Capability * cl_list;
当然这段代码并不是完全可移植的：P
used so forgot all about it. I have never actually seen code that used bitfields, and that isn''t the only strange thing it does:
What do you find strange?
/* An array of seven (7--I''m cheating) bytes naming the capability if
* it is not a pointer: */
u_char c_name[1];
That''s an array of *one* type ''u_char'' object.
/* The length and address of the capability list if this is a pointer: */
u_short cl_len;
struct Capability *cl_list;
Of course this code is not meant to be exactly portable :P
如果''u_char''和''u_short''是标准
类型的typedef，那么是的，它是可移植的。
-Mike
If ''u_char'' and ''u_short'' are typedefs for standard
types, then yes, it''s portable.
-Mike
" Noah Roberts" < NR ****** @ dontemailme.com>在消息中写道
news：bl ********** @ quark.scn.rain.com ...
"Noah Roberts" <nr******@dontemailme.com> wrote in message
news:bl**********@quark.scn.rain.com...
这是我第一次有看到这样的代码，我不知道它意味着什么。它似乎是C代码，但我认为我熟悉大多数构造......一定是错过了一个：
u_char c_perm：3;
这个声明是一个结构体内部以及以类似方式声明的其他几个变量。
我假设u_char是unsigned char的typedef，但是什么是
" ：3部分在那里做什么，这是什么意思？这是来自C99的新语法还是一直存在，我以前从未碰到它？
This is the first time I have seen code like this and I don''t know what
it means. It appears to be C code but I thought I was familiar with
most constructs...must have missed one:
u_char c_perm : 3;
This declairation is inside of a struct along with several other
variables declaired in a similar manner.
I am assuming u_char to be a typedef for unsigned char, but what is the
" : 3" part doing there and what does it mean? Is this new syntax from
C99 or has it always been around and I just never ran into it before?
它已经存在了很长一段时间。查找''bitfield''。
-Mike
It''s been around quite a while. Look up ''bitfield''.
-Mike
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