Howto“goto address_x;” [英] Howto "goto address_x;"
问题描述
在开始之前，请不要讨论goto是否是邪恶的。
对于生成的代码，这可能非常有意义。
知道如何让C转到
一个已分配给变量的地址，即
MyLabel会很有趣：
....
address_x = MyLabel;
....
goto address_x;
我试图将这些头寸打包成一个开关声明，然后将'b $ b''地址_x''变成'enum''类型的变量，例如
enum {Label1，Label2，Label3，...} address_x;
GotoStartPoint：
switch（address_x）{
case Label1：...
case Label2：...
case Label3：...
}
....
address_x = Label2;
转到GotoStartPoint;
但是当我看到汇编程序代码，它不如跳转到分配给av的地址那样有效ariable。
有没有什么办法可以获得好处？
最好的问候
弗兰克
Before I start, please let''s not discuss whether goto is evil or not.
For generated code, this can make perfect sense.
It would be interesting to know a trick how to get C to do a goto to
an address that has been assigned to a variable, i.e.
MyLabel:
....
address_x = MyLabel;
....
goto address_x;
I tried to pack the positions into a switch statement and made
''address_x'' a variable of type ''enum'', such as
enum { Label1, Label2, Label3, ... } address_x;
GotoStartPoint:
switch( address_x ) {
case Label1: ...
case Label2: ...
case Label3: ...
}
....
address_x = Label2;
goto GotoStartPoint;
But when I look at the assembler code, it is not as efficient as a
jump to an address assigned to a variable.
Is there any way to get arround that?
Best Regards
Frank
推荐答案
Frank写道：
Frank wrote:
知道一个技巧怎么样会很有趣让C做一个转到
已分配给变量的地址，即
It would be interesting to know a trick how to get C to do a goto to
an address that has been assigned to a variable, i.e.
（剪断有些令人困惑的代码）。 br />
您/实际上/想要实现的目标是什么？剪切的代码看起来像
试图解决一些你还没解释过的问题。
(snip somewhat confusing code).
What are you /actually/ trying to achieve ? The snipped code looks like
an attempt to solve some problem or other which you haven''t explained.
1月4日，12： 49 * am，Frank< fsch ... @ googlemail.comwrote：
On Jan 4, 12:49*am, Frank <fsch...@googlemail.comwrote:
在开始之前，*请不要讨论goto是否是邪恶的。
对于生成的代码，这可能非常有意义。
知道一个如何让C转到
已分配给变量的地址，即
MyLabel：
...
* * * address_x = MyLabel;
...
* * *转到地址_x;
我试图打包这些职位转换成一个switch语句并使得'b $ b''address_x''变量类型为''enum''，例如
enum {Label1，Label2，Label3 ，...} address_x;
GotoStartPoint：
switch（address_x）{
case Label1：...
ca se Label2：...
case Label3：...}
...
address_x = Label2;
转到GotoStartPoint;
但是当我查看汇编程序代码时，它的效率不如
跳转到分配的地址变量。
有没有什么方法可以得到它？
Before I start, *please let''s not discuss whether goto is evil or not.
For generated code, this can make perfect sense.
It would be interesting to know a trick how to get C to do a goto to
an address that has been assigned to a variable, i.e.
MyLabel:
...
* * *address_x = MyLabel;
...
* * *goto address_x;
I tried to pack the positions into a switch statement and made
''address_x'' a variable of type ''enum'', such as
enum { Label1, Label2, Label3, ... } address_x;
GotoStartPoint:
switch( address_x ) {
case Label1: ...
case Label2: ...
case Label3: ...}
...
address_x = Label2;
goto GotoStartPoint;
But when I look at the assembler code, it is not as efficient as a
jump to an address assigned to a variable.
Is there any way to get arround that?
在写协同程序之前，问问自己，它真的值得吗？
毕竟，有人将不得不保持它。
无论如何，这将显示你的目标：
http://www.google.com/search?hl=en&q=coroutines
" Frank" < fs ***** @ googlemail.com写信息
新闻：a2 ************************* ********* @ e6g2000p rf.googlegroups.com ...
"Frank" <fs*****@googlemail.comwrote in message
news:a2**********************************@e6g2000p rf.googlegroups.com...
在开始之前，请不要讨论goto是否是邪恶的或者没有。
对于生成的代码，这可能非常有意义。
知道一个如何让C去做goto的技巧会很有趣
已分配给变量的地址，即
MyLabel：
...
address_x = MyLabel;
...
转到地址_x;
我试图将这些头寸打包成一个开关声明并且制作了
''address_x'''enum''类型的变量，例如
enum {Label1，Label2，Label3，... } address_x;
GotoStartPoint：
开关（address_x）{
case Label1：...
case Label2：...
case Label3：...
}
...
address_x = Label2;
转到GotoStartPoint;
但是当我查看汇编程序代码时，它的效率不如
跳转到分配给变量的地址。
有没有什么方法可以获得它的好处？
最好的问候
Frank
Before I start, please let''s not discuss whether goto is evil or not.
For generated code, this can make perfect sense.
It would be interesting to know a trick how to get C to do a goto to
an address that has been assigned to a variable, i.e.
MyLabel:
...
address_x = MyLabel;
...
goto address_x;
I tried to pack the positions into a switch statement and made
''address_x'' a variable of type ''enum'', such as
enum { Label1, Label2, Label3, ... } address_x;
GotoStartPoint:
switch( address_x ) {
case Label1: ...
case Label2: ...
case Label3: ...
}
...
address_x = Label2;
goto GotoStartPoint;
But when I look at the assembler code, it is not as efficient as a
jump to an address assigned to a variable.
Is there any way to get arround that?
Best Regards
Frank
GNU C具有标签变量的扩展名，允许您跳转到任何
这样的评估地址。
标签作为价值
================
您可以使用一元运算符&&来获取当前函数
（或包含函数）中定义的标签的地址。值为
类型`void *''。该值是常量，可以在该类型的
常量有效的任何地方使用。例如：
void * ptr;
/ * ... * /
ptr =&& foo;
要使用这些值，您需要能够跳转到一个。这是用计算的goto语句（1），`goto * EXP;''完成的
。例如，
goto * ptr;
允许任何类型为void *的表达式。
使用这些常量的一种方法是初始化一个静态数组
作为跳转表：
static void * array [ ] = {&& foo，&& bar，&& hack};
然后您可以选择带索引的标签，如下所示：
goto * array [i];
GNU C has the extension of label variables and allows you to jump to any
such evaluated address.
Labels as Values
================
You can get the address of a label defined in the current function
(or a containing function) with the unary operator `&&''. The value has
type `void *''. This value is a constant and can be used wherever a
constant of that type is valid. For example:
void *ptr;
/* ... */
ptr = &&foo;
To use these values, you need to be able to jump to one. This is
done with the computed goto statement(1), `goto *EXP;''. For example,
goto *ptr;
Any expression of type `void *'' is allowed.
One way of using these constants is in initializing a static array
that will serve as a jump table:
static void *array[] = { &&foo, &&bar, &&hack };
Then you can select a label with indexing, like this:
goto *array[i];
这篇关于Howto“goto address_x;”的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
