将函数转换为宏 [英] Converting a function to a macro
问题描述
大家好，
今天我正在接近Code Project的精彩社区，关于用C / C ++重写函数作为宏的问题。
我目前正在学习C（和C ++），作为一项帮助我学习更多内容的活动，我正在编写一个程序，它将获取一个文件并读取它，然后将数据显示在一个对用户有用的方式。该项目可能相当无用，但到目前为止，已经值得。 （我已经能够学习文件I / O，并且我可以自由学习指针的基础知识，这样我就可以更多地了解文件I / O如何在C / C ++中工作）
现在，为了解决这个问题：
我写了一个函数，它接受一个字符串，并根据一个令牌爆炸它（是的） ，我知道有tokstr，但同样，这是为了学习）。我最近一直在阅读有关宏的内容，我对它们的看法不一。
一方面，人们说是的，使用宏[如果你计划重用代码]，另一方面，人们说不，在C ++中应该避免使用宏，所以我有点想弄清楚，我是否应该花时间编写宏来替换这个函数？
其次，我想知道（即使我不打算为这个函数编写宏），我应该避免在宏中做什么？我还读过你应该在你的宏中包围代码，用do / while循环，是否有特定原因？
我为此道歉很长的问题，但希望我能得到一些帮助。
圣帕特里克节快乐，
Gigabyte Giant
Hello all,
Today I am approaching the wonderful community of Code Project, with a question about rewriting functions as macros in C/C++.
I'm currently learning C (and C++), and, as an activity to help me learn more, I'm writing a program that'll take a file, and read it, and then display the data in a way that is useful to the user. The project might be fairly useless, but so far, it has been worth it. (I've been able to learn File I/O, and I took the liberty of learning the basics of pointers, so that I would understand more about how File I/O works in C/C++)
Now, to get to the point of this question:
I wrote a function, that takes a string, and "explodes" it, based on a token (yes, I know there is tokstr, but again, this is for learning). I've been reading about macros lately, and I've gotten mixed-opinions about them.
On one hand, people say "yes, use macros [if you plan on reusing the code]", and on the other, people say "no, macros should be avoided in C++", so I'm sort of trying to figure out, should I invest time in writing a macro to replace this function?
Secondly, I'd like to know (even if I'm not going to write a macro for this function), what should I refrain from doing in a macro? I've also read that you should surround code in your macro(s), with a do/while loop, is there a specific reason?
I do apologize for the long question, but hopefully I'll be able to get some help.
Happy St. Patrick's Day,
Gigabyte Giant
推荐答案
为什么宏是好的？
1.避免重复打字（减少出错的风险）。
示例：因此，MFC，boost和ATL / WTL使用宏。
2.使用完全不同的行为来编写现有代码。
示例：模拟测试设施;交换新的定义和删除堆调试。
3.生成代码 - 源代码不适合手工编辑。
为什么宏不好？
1.对调试产生不利影响。
a。单步通过宏扩展到十几行。
b。在宏定义上设置一个断点。
2.隐藏 - 宏可以隐藏你的东西 - 使调试和代码审查更加困难。
示例：#define true false
3.欺骗现有代码，使用截然不同的行为进行编译。
4.宏不限于命名空间。
返回当天 - 内联函数之前 - 定义的函数作为一个宏是一种内联代码而不是普通函数调用的方法。使用__inline关键字，这个宏的使用已经过时。
摘要
仅使用宏如果绝对需要并且只有在没有其他机制的情况下。相反，对类型和常量/文字使用const，enum和typedef。
您将函数重写为宏的兴趣作为学习练习具有很大的价值但没有更多。一旦你开始使用其他宏定义宏，你也会发现一些惊喜。
完成学习宏之后，你最终可以使用C ++模板 - 这是比宏更强大 - 但可以限制在命名空间。
祝你好运。
Why macros are good?
1. avoid repetitive typing (less risk of mistakes).
Examples: MFC, boost and ATL/WTL use macros for this reason.
2. trick existing code to be compiled with wildly different behavior.
Examples: Mock facilities for testing; swapping out definitions of new and delete for heap debugging.
3. generated code - source code not meant for hand-editing.
Why macros are bad?
1. Adversely impacts debugging.
a. single-step through a macro that expands to a dozen lines.
b. set a break point on a macro definition.
2. Hiding - macros can hide things from you - to make debugging and code review more difficult.
Example: #define true false
3. Trick existing code to be compiled with wildly different behavior.
4. Macros are not confined to a namespace.
Back in the day - before inline functions - a function defined as a macro was a way to have inline code instead of a plain function call. With the __inline keyword, this use of a macro is obsolete.
Summary
Use a macro only if absolutely needed and only if there is no other mechanism. Instead, use const, enum, and typedef for types and constants / literals.
Your interest in re-writing a function as a macro has much value as a learning exercise but no more. You will also find a few surprises once you start defining macros using other macros.
After you're done learning macros, you can eventually play with C++ templates - which are more more powerful than macros - but can be confined to a namespace.
Good luck.
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