使用全局变量的最优雅方法是什么？ [英] What is the most elegant way to work with global variables?

问题描述

几年前，我了解到全局变量是不好的，应该避免。但是我知道它们有时是不可避免的，至少在嵌入式系统中是如此。您认为与他们合作的最优雅的方式是什么？

A couple years ago I learned that global variables are bad and should be avoided. But I know they are sometimes unavoidable, at least in an embedded system. What do you think is the most elegant way to work with them?

在我的项目中，我有一个名为 globals.h ，其中定义了所有全局变量：

In my projects I have a file called globals.h where I define all my global variables:

#ifndef GLOBALS_H
#define GLOBALS_H
extern int16_t    gVariable1;
extern int16_t    gVariable2;
….
#endif

在我的主项目文件中，我声明了所有全局变量：

In my main project file I declare all global variables:

/*
***********************************************************************
*                            global variables                         *
***********************************************************************
*/
    int16_t     gVariable1 = 0;
    int16_t     gVariable2 = 0;


int16_t main (void)
{
    gVariable1 = 6;

    //  do other stuff
}

知道我在需要访问全局变量的项目的每个其他文件中包含 globals.h 。

And know I include globals.h in every other file of the project which needs access to a global variable.

那很好，但是还有一种更优雅的方式来处理该问题吗？

That works fine, but is there a more elegant way to handle that?

推荐答案

我不确定全局变量在所有情况下都是不好的，但是您真的需要努力使它们很少（否则，您的代码不可读）。例如，< stdio.h> 具有 stdout ，如果将其替换为某些内容将不会更好。 FILE * get_standard_output（void）; getter函数。

I am not sure that global variables are bad in all cases, but you really need to work hard to have very few of them (otherwise, your code in unreadable). For example <stdio.h> has stdout, and it won't be better if it was replaced by some FILE*get_standard_output(void); getter function.

根据经验，请避免超过4个或整个程序中的5个全局变量（将神奇数字7 称为提示（关于我们的认知限制）。

As a rule of thumb, avoid having more than 4 or 5 global variables in your entire program (recall the magical number seven as a hint on our cognitive limitations).

但是，您可以打包（巧妙并具有良好的品味，使代码易于阅读）几个相关的 全局变量转换为 struct 类型的单个变量。以您的示例为例，这可能意味着您的 globals.h ：

However, you could pack (cleverly and with good taste, to keep your code readable) several related global variables into a single one of struct type. With your example, that could mean in your globals.h:

struct globalstate_st { int16_t v1, v2; };

然后

extern struct globalstate_st gs;

，您应该使用 gs.v1 gVariable1 ；如果使用优化进行编译，则使用 gs.v1 的性能等同于使用 gVariable1 。

and you would use gs.v1 instead of gVariable1; if you compile with optimizations, the performance of using gs.v1 is equivalent to using gVariable1.

BTW，如果您有多线程程序，通常应该使用互斥体（或其他某种同步或原子性）。考虑阅读此pthread教程。

BTW, if you have a multi-threaded program, you generally should protect global data with some mutex (or some other kind of synchronization or atomicity). Consider reading this pthread tutorial.

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