多行 DEFINE 指令?-C/C++问题

Multi-line DEFINE directives?(多行 DEFINE 指令?)

本文介绍了多行 DEFINE 指令?的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

我不是专家，所以请放轻松.这两个代码段有什么区别吗?

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;

和

#define BIT3 (0x1 << 3) static int a;

另外，有没有办法在一行中写第一个?这种多线样式的意义何在?下面的代码好吗?

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;

推荐答案

如果您有一个非常复杂的宏，如果它全部在一行上将难以阅读(尽管不建议使用多行宏)非常复杂的宏).

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).

一般来说，您可以使用续行字符编写多行定义.所以例如

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
", 
    5 
    )

但是你不能在你的第一个例子中做到这一点.你不能像那样拆分令牌；<< 左移运算符必须始终在没有任何分隔空格的情况下编写，否则它将被解释为两个小于运算符.所以也许:

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;

现在相当于你的第二个例子.

which is now equivalent to your second example.

[虽然我不确定那个宏会有什么用处！]

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