多行DEFINE指令? [英] Multi-line DEFINE directives?
问题描述
我不是专家,这样下去容易对我。在这两个code段之间有什么区别?
的#define BIT3(为0x1
<
<
3)
静态int类型的;
和
的#define BIT3(为0x1< 3;)静态int类型的;
此外,有没有先写在一行中的方法吗?什么是这种多线样式的地步?在下面的code好?
的#define BIT3(为0x1< 3;)
静态int类型的;
如果你有一个非常复杂的宏这将是难以阅读,如果它是全部在一行上(虽然它不可取的多行宏是有用的非常复杂的宏)
在一般情况下,你可以写使用行继续符, \\
多行定义。因此,例如
的#define MY_MACRO的printf(\\
我喜欢%D型奶酪的\\ n,\\
5 \\
)
但你不能这样做,你的第一个例子。你可以不拆这样的标记;在<<
左移位运算符必须始终没有任何空格分开写,否则会间preTED为两个低于运营商。因此,也许:
的#define BIT3(为0x1 \\
<< \\
3)\\
静态int类型的;
这是现在相当于你的第二个例子。
的 [虽然我不知道如何宏将永远是有用的!] 的
I am not an expert, so go easy on me. Are there any differences between these two code segments?
#define BIT3 (0x1
<
<
3)
static int a;
and
#define BIT3 (0x1 << 3) static int a;
Also, is there a way to write the first in one line? What is the point of this multi-line style? Is the following code good?
#define BIT3 (0x1 << 3)
static int a;
A multi-line macro is useful if you have a very complex macro which would be difficult to read if it were all on one line (although it's inadvisable to have very complex macros).
In general, you can write a multi-line define using the line-continuation character, \
. So e.g.
#define MY_MACRO printf( \
"I like %d types of cheese\n", \
5 \
)
But you cannot do that with your first example. You cannot split tokens like that; the <<
left-shift operator must always be written without any separating whitespace, otherwise it would be interpreted as two less-than operators. So maybe:
#define BIT3 (0x1 \
<< \
3) \
static int a;
which is now equivalent to your second example.
[Although I'm not sure how that macro would ever be useful!]
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