空陈述 [英] Empty statement
问题描述
您好，
我希望有类似的东西
#ifdef VERSION_DEBUG
#define DEBUG（x）DebugFnc （x）
#end
#ifdef VERSION_RELEASE
#define DEBUG（x）< empty-statement>
#end
但是我不知道如何实现空语句..问题，
课程是在当宏被调用时，额外的分号，
DEBUG（x）;在发布版本中。其中一个可能的解决方案是设置
#define DEBUG（x）do {} while（0）
但我不确定编译器是否足够智能
来优化它。还有其他任何想法吗？
-
Maksim Sipos
Hello,
I would like to have something like
#ifdef VERSION_DEBUG
#define DEBUG(x) DebugFnc(x)
#end
#ifdef VERSION_RELEASE
#define DEBUG(x) <empty-statement>
#end
but I''m not sure how to implement the empty statement.. the problem, of
course is in the extra semicolon when the macro is called as in,
DEBUG(x); in release version. One of the possible solutions is to set
#define DEBUG(x) do{}while(0)
but I am not sure whether the compiler is smart enough
to optimize this. Any other ideas, comments?
--
Maksim Sipos
推荐答案
怎么样：
#define DEBUG（x）;
这有用吗？
-
gabriel
What about:
#define DEBUG(x) ;
Does this work?
--
gabriel
Maksim Sipos写道：
Maksim Sipos wrote:
您好，
我想要一些像
#ifdef VERSION_DEBUG
#define DEBUG（x）DebugFnc（x）
#end
#ifdef VERSION_RELEASE
#define DEBUG（x）< empty-statement>
#end
但我不知道如何实现空语句..当问题调用宏时，问题当然是在额外的分号中，
DEBUG（x）;在发布版本。
Hello,
I would like to have something like
#ifdef VERSION_DEBUG
#define DEBUG(x) DebugFnc(x)
#end
#ifdef VERSION_RELEASE
#define DEBUG(x) <empty-statement>
#end
but I''m not sure how to implement the empty statement.. the problem, of
course is in the extra semicolon when the macro is called as in,
DEBUG(x); in release version.
[...]
只需将其定义为空：
#define DEBUG（x）
为什么是额外的分号？发布版本中的一个问题？
你可以提供一些不起作用的代码示例吗？
-
+ --------- + ----------------------------- ----- + ----------------------------- +
|肯尼斯| kenbrody at spamcop.net | 表达的意见|
| J. | http://www.hvcomputer.com |这里不一定是|
|布罗迪| http://www.fptech.com |那些fP技术。 |
+ --------- + ------------------------------ ---- + ----------------------------- +
[...]
Simply define it as nothing:
#define DEBUG(x)
Why is "the extra semicolon" a problem in the release version?
Can you give a sample of code where it doesn''t work?
--
+---------+----------------------------------+-----------------------------+
| Kenneth | kenbrody at spamcop.net | "The opinions expressed |
| J. | http://www.hvcomputer.com | herein are not necessarily |
| Brody | http://www.fptech.com | those of fP Technologies." |
+---------+----------------------------------+-----------------------------+
Maksim Sipos写道：
Maksim Sipos wrote:
你好，
我想有类似的东西
#ifdef VERSION_DEBUG
#define DEBUG（x）DebugFnc（x）
#end
#ifdef VERSION_RELEASE
#define DEBUG（x）< empty-statement>
#end
所需要的只是
#define DEBUG（x）/ *这里没什么* /
但是我''我不确定如何实现空语句..问题，当然，在调用宏时，在额外的分号中，
DEBUG（x）;在发布版本中。
分号不会引起任何问题，因为它本身就是一个有效的空
语句。例如
int foo（无效）
{
int i; ; ; ;;;;
;
;;;;
for（i = 0; i< 10; ++ i）;
if（i> 10）{
;
}
返回i;
}
完全合法。现在，想象一下，每个分号上面没有
终止语句的是DEBUG（无论如何）。
其中一个可能的解决方案是设置
#define DEBUG（x）do {} while（0）
但我不确定编译器是否足够聪明以优化它。还有其他任何想法，评论吗？
Hello,
I would like to have something like
#ifdef VERSION_DEBUG
#define DEBUG(x) DebugFnc(x)
#end
#ifdef VERSION_RELEASE
#define DEBUG(x) <empty-statement>
#end
All that is required is
#define DEBUG(x) /* nothing here */
but I''m not sure how to implement the empty statement.. the problem, of
course is in the extra semicolon when the macro is called as in,
DEBUG(x); in release version.
The semicolon will not cause any problems since it is itself a valid "empty"
statement. For example
int foo(void)
{
int i; ; ; ;;;;
;
;;;;
for(i=0; i<10; ++i);
if(i > 10){
;
}
return i;
}
is perfectly legal. Now, imagine that each semicolon above which does not
terminate a statement is proceeded by DEBUG(whatever).
One of the possible solutions is to set
#define DEBUG(x) do{}while(0)
but I am not sure whether the compiler is smart enough
to optimize this. Any other ideas, comments?
这个陈述不应该被优化掉，因为意图是执行
do-while *至少*一次。这实际上是实现
调试宏的一种非常好的方法，因为它可以防止悬空的其他问题以及
为调试特定的变量引入了一个范围。例如，
if（pred）
DEBUG（stuff）;
else
return 0;
如果你定义了
#define DEBUG（x）if（dbgEnabled）fprintf（stderr，" DBG： x =％d \ n"，x）
你会遇到问题。
/ david
-
安德烈，一个简单的农民，只有一件事在他的脑海中悄悄地沿着东墙悄悄地上涨：''安德烈，蠕动...安德烈，蠕动...安德烈，蠕动。''
- 未知
This statement should not be optimized away since the intent is to execute the
do-while *at least* once. This is actually a very good way to implement
debugging macros since it protects against the dangling else problem as well as
introduces a scope for debugging-specific variables. For example,
if(pred)
DEBUG(stuff);
else
return 0;
If you''ve defined
#define DEBUG(x) if(dbgEnabled) fprintf(stderr, "DBG: x=%d\n", x)
you''ll run into problems.
/david
--
Andre, a simple peasant, had only one thing on his mind as he crept
along the East wall: ''Andre, creep... Andre, creep... Andre, creep.''
-- unknown
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