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[Translated] Translated by Cycoe
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[#]: collector: (lujun9972)
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[#]: translator: (cycoe)
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[#]: reviewer: ( )
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[#]: publisher: ( )
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[#]: url: ( )
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[#]: subject: (Debugging in Emacs: The Grand Unified Debugger)
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[#]: via: (https://opensourceforu.com/2019/09/debugging-in-emacs-the-grand-unified-debugger/)
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[#]: author: (Vineeth Kartha https://opensourceforu.com/author/vineeth-kartha/)
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Debugging in Emacs: The Grand Unified Debugger
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======
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[![][1]][2]
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_This article briefly explores the features of the Grand Unified Debugger, a debugging tool for Emacs._
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If you are a C/C++ developer, it is highly likely that you have crossed paths with GDB (the GNU debugger) which is, without doubt, one of the most powerful and unrivalled debuggers out there. Its only drawback is that it is command line based, and though that offers a lot of power, it is sometimes a bit restrictive as well. This is why smart people started coming up with IDEs to integrate editors and debuggers, and give them a GUI. There are still developers who believe that using the mouse reduces productivity and that mouse-click based GUIs are temptations by the devil.
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Since Emacs is one of the coolest text editors out there, I am going to show you how to write, compile and debug code without having to touch the mouse or move out of Emacs.
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![Figure 1: Compile command in Emacs’ mini buffer][3]
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![Figure 2: Compilation status][4]
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The Grand Unified Debugger, or GUD as it is commonly known, is an Emacs mode in which GDB can be run from within Emacs. This provides all the features of Emacs in GDB. The user does not have to move out of the editor to debug the code written.
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**Setting the stage for the Grand Unified Debugger**
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If you are using a Linux machine, then it is likely you will have GDB and gcc already installed. The next step is to ensure that Emacs is also installed. I am assuming that the readers are familiar with GDB and have used it at least for basic debugging. If not, please do check out some quick introductions to GDB that are widely available on the Internet.
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For people who are new to Emacs, let me introduce you to some basic terminology. Throughout this article, you will see shortcut commands such as C-c, M-x, etc. C means the Ctrl key and M means the Alt key. C-c means the Ctrl + c keys are pressed. If you see C-c c, it means Ctrl + c is pressed followed by c. Also, in Emacs, the main area where you edit the text is called the main buffer, and the area at the bottom of the Emacs window, where commands are entered, is called the mini buffer.
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Start Emacs and to create a new file, press _C-x C-f_. This will prompt you to enter a file name. Let us call our file ‘buggyFactorial.cpp’. Once the file is open, type in the code shown below:
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```
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#include<iostream>
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#include <assert.h>
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int factorial(int num) {
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int product = 1;
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while(num--) {
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product *= num;
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}
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return product;
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}
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int main() {
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int result = factorial(5);
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assert(result == 120);
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}
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```
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Save the file with _C-x C-s_. Once the file is saved, it’s time to compile the code. Press _M-x_ and in the prompt that comes up, type in compile and hit Enter. Then, in the prompt, replace whatever is there with _g++ -g buggyFactorial.cpp_ and again hit _Enter_.
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This will open up another buffer in Emacs that will show the status of the compile and, hopefully, if the code typed in is correct, you will get a buffer like the one shown in Figure 2.
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To hide this compilation status buffer, make sure your cursor is in the compilation buffer (you can do this without the mouse using _C-x o_-this is used to move the cursor from one open buffer to the other), and then press _C-x 0_. The next step is to run the code and see if it works fine. Press M-! and in the mini buffer prompt, type _./a.out._
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See the mini buffer that says the assertion is failed. Clearly, something is wrong with the code, because the factorial (5) is 120. So let’s debug the code now.
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![Figure 3: Output of the code in the mini buffer][5]
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![Figure 4: The GDB buffer in Emacs][6]
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**Debugging the code using GUD**
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Now, since we have the code compiled, it’s time to see what is wrong with it. Press M-x and in the prompt, enter _gdb._ In the next prompt that appears, write _gdb -i=mi a.out_, which will start GDB in the Emacs buffer and if everything goes well, you should get the window that’s shown in Figure 4.
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At the gdb prompt, type break main and then r to run the program. This should start running the program and should break at the _main()_.
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As soon as GDB hits the break point at main, a new buffer will open up showing the code that you are debugging. Notice the red dot on the left side, which is where your breakpoint was set. There will be a small indicator that shows which line of the code you are on. Currently, this will be the same as the break point itself (Figure 5).
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![Figure 5: GDB and the code in split windows][7]
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![Figure 6: Show the local variables in a separate frame in Emacs][8]
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To debug the factorial function, we need to step into it. For this, you can either use the _gdb_ prompt and the gdb command step, or you can use the Emacs shortcut _C-c C-s_. There are other similar shortcuts, but I prefer using the GDB commands. So I will use them in the rest of this article.
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Let us keep an eye on the local variables while stepping through the factorial number. Check out Figure 6 for how to get an Emacs frame to show the local variables.
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Step through the code in the GDB prompt and watch the value of the local variable change. In the first iteration of the loop itself, we see a problem. The value of the product should have been 5 and not 4.
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This is where I leave you and now it’s up to the readers to explore and discover the magic land called GUD mode. Every gdb command works in the GUD mode as well. I leave the fix to this code as an exercise to readers. Explore and see how you can customise things to make your workflow simpler and become more productive while debugging.
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--------------------------------------------------------------------------------
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via: https://opensourceforu.com/2019/09/debugging-in-emacs-the-grand-unified-debugger/
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作者：[Vineeth Kartha][a]
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选题：[lujun9972][b]
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://opensourceforu.com/author/vineeth-kartha/
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[b]: https://github.com/lujun9972
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[1]: https://i0.wp.com/opensourceforu.com/wp-content/uploads/2019/09/Screenshot-from-2019-09-25-15-39-46.png?resize=696%2C440&ssl=1 (Screenshot from 2019-09-25 15-39-46)
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[2]: https://i0.wp.com/opensourceforu.com/wp-content/uploads/2019/09/Screenshot-from-2019-09-25-15-39-46.png?fit=800%2C506&ssl=1
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[3]: https://i1.wp.com/opensourceforu.com/wp-content/uploads/2019/09/Figure_1.png?resize=350%2C228&ssl=1
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[4]: https://i2.wp.com/opensourceforu.com/wp-content/uploads/2019/09/Figure_2.png?resize=350%2C228&ssl=1
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[5]: https://i0.wp.com/opensourceforu.com/wp-content/uploads/2019/09/Figure_3.png?resize=350%2C228&ssl=1
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[6]: https://i0.wp.com/opensourceforu.com/wp-content/uploads/2019/09/Figure_4.png?resize=350%2C227&ssl=1
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[7]: https://i1.wp.com/opensourceforu.com/wp-content/uploads/2019/09/Figure_5.png?resize=350%2C200&ssl=1
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[8]: https://i1.wp.com/opensourceforu.com/wp-content/uploads/2019/09/Figure_6.png?resize=350%2C286&ssl=1
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@ -0,0 +1,101 @@
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[#]: collector: (lujun9972)
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[#]: translator: (cycoe)
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[#]: reviewer: ( )
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[#]: publisher: ( )
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[#]: url: ( )
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[#]: subject: (Debugging in Emacs: The Grand Unified Debugger)
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[#]: via: (https://opensourceforu.com/2019/09/debugging-in-emacs-the-grand-unified-debugger/)
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[#]: author: (Vineeth Kartha https://opensourceforu.com/author/vineeth-kartha/)
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Emacs 调试秘籍之——GUD 调试器
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======
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[![][1]][2]
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_本文简短地对 Emacs 的调试工具 GUD（译注：全称 Grand Unified Debugger，鉴于其缩写形式更为人熟知，以下全文将使用缩写替代此全称）的特性进行了探索。_
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如果你是一个 C 或 C++ 开发者，你很可能已经使用过 GDB（GNU 调试器），毫无疑问，它是现今最强大、最无可匹敌的调试器之一。它唯一的缺点就是它基于命令行，虽然仍能提供许多强大的功能，但有时也会具有一些局限性。这也就是为什么聪明的人们开始追求整合了编辑器和调试器的<ruby>图形化<rt>GUI</rt>集成<rt>Integrated</rt>开发<rt>Development</rt>环境<rt>Environment</rt></ruby>。仍有些开发者坚信使用鼠标会降低工作效率，在 GUI 上用鼠标点～点～点～是来自恶魔的诱惑。
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因为 Emacs 是现今最酷的文本编辑器之一，我将为你展示如何在不碰鼠标且不离开 Emacs 的情况下，实现写代码、编译代码、调试代码的过程。
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![图 1: Emacs 迷你缓冲区中的编译命令][3]
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![图 2: 编译状态][4]
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GUD 是 Emacs 下的一个<ruby>模式<rt>mode</rt></ruby>，用于在 Emacs 中运行 GDB。它向 GDB 提供了 Emacs 的所有特性，使用户无需离开编辑器就可以对代码进行调试。
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**使用 GUD 的前期准备**
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如果你正在使用一个 Linux 机器，很可能你已经安装了 GDB 和 gcc，接下来就是要确保已经安装了 Emacs。以下的内容我将假设读者熟悉 GDB 并且至少用它做过基本的调试。如果你未曾接触过 GDB，你可以做个快速入门，这些资料在网上随处可得。
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对于那些 Emacs 新手，我将向你介绍一些基本术语。纵览整篇文章，你将看到诸如 _C-c M-x_ 等快捷键。此处 _C_ 代表 _Ctrl_ 键，_M_ 代表 _Alt_ 键。_C-c_ 代表 _Ctrl_ 键和 _c_ 键被同时按下。如果你看到 _C-c c_，它代表同时按下 _Ctrl_ 键和 _c_ 键，紧接着按下 _c_ 键。在 Emacs 中，编辑文本的主要区域被称为<ruby>主<rt>main</rt>缓冲区<rt>buffer</rt></ruby>，而在 Emacs 窗口下方用于输入命令的区域被称为<ruby>迷你<rt>mini</rt>缓冲区<rt>buffer</rt></ruby>。
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启动 Emacs，并按下 _C-x C-f_ 来创建一个新文件。Emacs 将提示你输入一个文件名，此处让我们将文件命名为 `buggyFactorial.cpp`。一旦文件打开，输入如下代码：
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```
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#include<iostream>
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#include <assert.h>
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int factorial(int num) {
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int product = 1;
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while(num--) {
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product *= num;
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}
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return product;
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}
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int main() {
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int result = factorial(5);
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assert(result == 120);
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}
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```
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使用 _C-x C-s_ 快捷键保存文件。文件保存完毕，是时候进行编译了。按下 _M-x_，在弹出的<ruby>提示符<rt>prompt</rt></ruby>后输入 _compile_ 并点击回车。然后在提示符后，将内容替换为 _g++ -g buggyFactorial.cpp_ 并再次点击回车。
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这将在 Emacs 中开启另一个缓冲区，显示编译的状态。如果你的代码输入没有错误，你将预期得到如图 2 所示的缓冲区。
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要想隐藏编译缓冲区，首先确保你的光标在编译缓冲区中（你可以不使用鼠标，而是通过 _C-x o_ 快捷键将光标从一个缓冲区移动到另一个），然后按下 _C-x 0_。下一步就是运行代码，并观察是否运行良好。按下 _M-!_ 快捷键并在迷你缓冲区的提示符后面输入 _./a.out_。
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你可以看到迷你缓冲区中显示断言失败。很明显代码中有错误，因为 5 的阶乘是 120。那么让我们现在开始调试吧。
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![图 3: 代码在迷你缓冲区中的输出][5]
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![图 4: Emacs 中的 GDB 缓冲区][6]
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**使用 GUD 调式代码**
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现在，我们的代码已经编译完成，是时候看看到底哪里出错了。按下 _M-x_ 快捷键并在提示符后输入 _gdb_。在接下来的提示符后，输入 _gdb -i=mi a.out_。如果一切顺利，GDB 会在 Emacs 缓冲区中启动，你会看到如图 4 所示的窗口。
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在 _gdb_ 提示符后，输入 _break main_ 来设置断点，并输入 _r_ 来运行程序。程序会开始运行并停在 _main()_ 函数处。
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一旦 GDB 到达了 _main_ 处设置的断点，就会弹出一个新的缓冲区显示你正在调试的代码。注意左侧的红点，正是你设置断点的位置，同时会有一个小的标志提示你当前代码运行到了哪一行。当前，该标志就在断点处（如图 5）。
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![图 5: GDB 与代码显示在两个分离的窗口][7]
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![图 6: 在 Emacs 中使用独立帧显示局部变量][8]
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为了调试 _factorial_ 函数，我们需要单步运行。想要达到此目的，你可以使用 _gdb_ 提示符和 GDB 命令 _step_，或者使用 Emacs 快捷键 _C-c C-s_。还有其它一些快捷键，但我更喜欢 GDB 命令。因此我将在本文的后续部分使用它们。
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单步运行时让我们注意一下局部变量中的阶乘值。参考图 6 来设置在 Emacs 帧中显示局部变量值。
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在 GDB 提示符中进行单步运行并观察局部变量值的变化。在循环的第一次迭代中，我们发现了一个问题。此处乘法的结果应该是 5 而不是 4。
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本文到这里也差不多结束了，读者可以自行探索发现 GUD 模式这片新大陆。GDB 中的所有命令都可以在 GUD 模式中运行。我将此代码的修复留给读者作为一个练习。看看你在调试的过程中，可以做哪一些定制化，来使你的工作流更加简单和高效。
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--------------------------------------------------------------------------------
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via: https://opensourceforu.com/2019/09/debugging-in-emacs-the-grand-unified-debugger/
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作者：[Vineeth Kartha][a]
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选题：[lujun9972][b]
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译者：[cycoe](https://github.com/cycoe)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://opensourceforu.com/author/vineeth-kartha/
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[b]: https://github.com/lujun9972
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[1]: https://i0.wp.com/opensourceforu.com/wp-content/uploads/2019/09/Screenshot-from-2019-09-25-15-39-46.png?resize=696%2C440&ssl=1 (Screenshot from 2019-09-25 15-39-46)
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[2]: https://i0.wp.com/opensourceforu.com/wp-content/uploads/2019/09/Screenshot-from-2019-09-25-15-39-46.png?fit=800%2C506&ssl=1
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[3]: https://i1.wp.com/opensourceforu.com/wp-content/uploads/2019/09/Figure_1.png?resize=350%2C228&ssl=1
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[4]: https://i2.wp.com/opensourceforu.com/wp-content/uploads/2019/09/Figure_2.png?resize=350%2C228&ssl=1
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[5]: https://i0.wp.com/opensourceforu.com/wp-content/uploads/2019/09/Figure_3.png?resize=350%2C228&ssl=1
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[6]: https://i0.wp.com/opensourceforu.com/wp-content/uploads/2019/09/Figure_4.png?resize=350%2C227&ssl=1
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[7]: https://i1.wp.com/opensourceforu.com/wp-content/uploads/2019/09/Figure_5.png?resize=350%2C200&ssl=1
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[8]: https://i1.wp.com/opensourceforu.com/wp-content/uploads/2019/09/Figure_6.png?resize=350%2C286&ssl=1
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