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[#]: subject: "Position text on your screen in Linux with ncurses"
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[#]: via: "https://opensource.com/article/21/8/ncurses-linux"
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[#]: author: "Jim Hall https://opensource.com/users/jim-hall"
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[#]: collector: "lujun9972"
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[#]: translator: "perfiffer"
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[#]: reviewer: " "
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[#]: publisher: " "
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[#]: url: " "
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Position text on your screen in Linux with ncurses
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======
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Use ncurses in Linux to place text at specific locations on the screen
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and enable more user-friendly interfaces.
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![Person using a laptop][1]
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Most Linux utilities just scroll text from the bottom of the screen. But what if you wanted to position text on the screen, such as for a game or a data display? That's where **ncurses** comes in.
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**curses** is an old Unix library that supports cursor control on a text terminal screen. The name _curses_ comes from the term _cursor control_. Years later, others wrote an improved version of **curses** to add new features, called _new curses_ or **ncurses**. You can find **ncurses** in every modern Linux distribution, although the development libraries, header files, and documentation may not be installed by default. For example, on Fedora, you will need to install the **ncurses-devel** package with this command:
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```
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`$ sudo dnf install ncurses-devel`
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```
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### Using ncurses in a program
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To directly address the screen, you'll first need to initialize the **ncurses** library. Most programs will do that with these three lines:
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* initscr(); Initialize the screen and the **ncurses** code
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* cbreak(); Disable buffering and make typed input immediately available
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* noecho(); Turn off echo, so user input is not displayed to the screen
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These functions are defined in the **curses.h** header file, which you'll need to include in your program with:
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```
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`#include <curses.h>`
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```
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After initializing the terminal, you're free to use any of the **ncurses** functions, some of which we'll explore in a sample program.
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When you're done with **ncurses** and want to go back to regular terminal mode, use **endwin();** to reset everything. This command resets any screen colors, moves the cursor to the lower-left of the screen, and makes the cursor visible. You usually do this right before exiting the program.
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### Addressing the screen
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The first thing to know about **ncurses** is that screen coordinates are _row,col_, and start in the upper-left at 0,0. **ncurses** defines two global variables to help you identify the screen size: LINES is the number of lines on the screen, and COLS is the number of columns. The bottom-right position is LINES-1,COLS-1.
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For example, if you wanted to move the cursor to line 10 and column 30, you could use the move function with those coordinates:
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```
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`move(10, 30);`
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```
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Any text you display after that will start at that screen location. To display a single character, use the **addch(c)** function with a single character. To display a string, use **addstr(s)** with your string. For formatted output that's similar to **printf**, use **printw(fmt, …)** with the usual options.
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Moving to a screen location and displaying text is such a common thing that **ncurses** provides a shortcut to do both at once. The **mvaddch(row, col, c)** function will display a character at screen location _row,col_. And the **mvaddstr(row, col, s)** function will display a string at that location. For a more direct example, using **mvaddstr(10, 30, "Welcome to ncurses");** in a program will display the text "Welcome to ncurses" starting at row 10 and column 30. And the line **mvaddch(0, 0, '+');** will display a single plus sign in the upper-left corner at row 0 and column 0.
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Drawing text to the terminal screen can have a performance impact on certain systems, especially on older hardware terminals. So **ncurses** lets you "stack up" a bunch of text to display to the screen, then use the **refresh()** function to make all of those changes visible to the user.
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Let's look at a simple example that pulls everything together:
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```
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#include <curses.h>
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int
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main()
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{
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initscr();
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cbreak();
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noecho();
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mvaddch(0, 0, '+');
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mvaddch(LINES - 1, 0, '-');
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mvaddstr(10, 30, "press any key to quit");
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refresh();
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getch();
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endwin();
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}
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```
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The program starts by initializing the terminal, then prints a plus sign in the upper-left corner, a minus in the lower-left corner, and the text "press any key to quit" at row 10 and column 30. The program gets a single character from the keyboard using the getch() function, then uses **endwin()** to reset the terminal before the program exits completely.
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**getch()** is a useful function that you could use for many things. I often use it as a way to pause before I quit the program. And as with most **ncurses** functions, there's also a version of **getch()** called **mvgetch(row, col)** to move to screen position _row,col_ before waiting for a character.
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### Compiling with ncurses
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If you tried to compile that sample program in the usual way, such as `gcc pause.c`, you'll probably get a huge list of errors from the linker. That's because the **ncurses** library is not linked automatically by the GNU C Compiler. Instead, you'll need to load it for linking using the `-l ncurses` command-line option.
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```
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`$ gcc -o pause pause.c -lncurses`
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```
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Running the new program will print a simple "press any key to quit" message that's more or less centered on the screen:
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![centered message in a program window][2]
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Figure 1: A centered "press any key to quit" message in a program.
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### Building better programs with ncurses
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Explore the **ncurses** library functions to learn about other ways to display text to the screen. You can find a list of all **ncurses** functions in the man ncurses manual page. This gives a general overview of **ncurses** and provides a table-like list of the different **ncurses** functions, with a reference to the manual page that has full details. For example, **printw** is described in the _curs_printw(3X)_ manual page, which you can view with:
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```
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`$ man 3x curs_printw`
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```
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or just:
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```
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`$ man curs_printw`
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```
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With **ncurses**, you can create more interesting programs. By printing text at specific locations on the screen, you can create games and advanced utilities to run in the terminal.
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--------------------------------------------------------------------------------
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via: https://opensource.com/article/21/8/ncurses-linux
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作者：[Jim Hall][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://opensource.com/users/jim-hall
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[b]: https://github.com/lujun9972
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[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/laptop_screen_desk_work_chat_text.png?itok=UXqIDRDD (Person using a laptop)
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[2]: https://opensource.com/sites/default/files/press-key_0.png
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@ -0,0 +1,130 @@
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[#]: sub·ject: "Position text on your screen in Linux with ncurses"
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[#]: via: "https://opensource.com/article/21/8/ncurses-linux"
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[#]: author: "Jim Hall https://opensource.com/users/jim-hall"
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[#]: collector: "lujun9972"
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[#]: translator: "perfiffer"
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[#]: reviewer: " "
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[#]: publisher: " "
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[#]: url: " "
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使用 ncurses 在你的 Linux 屏幕上定位文本
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======
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使用 ncurses 在 Linux 屏幕上的特定位置放置文本，可以带来更友好的用户界面体验。
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![Person using a laptop][1]
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大多数的 Linux 实用程序仅仅只在屏幕的底部滚动文本。如果你想在屏幕中放置你的文本，例如一个游戏或者一个数据展示，你可以试试 **ncurses**。
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**curses** 是一个旧的 Unix 库，它可以在文本终端界面控制光标。curses 的名称就来自于术语 cursor control。多年以后，其他人编写了新的 **curses** 版本用来添加新的功能，新版本被叫做 new curses 或者 **ncurses**。你可以在每个流行的 Linux 发行版中找到 ncurses。尽管默认情况下可能未安装开发库、头文件和文档。例如，在 Fedora 上，你需要使用以下命令安装 **ncurses-devel** 包：
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```
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$ sudo dnf install ncurses-devel
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```
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### 在程序中使用 ncurses
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要在屏幕上直接寻址，你首先需要初始化 **ncurses** 库。大部分程序会通过以下三行来做到这一点：
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* initscr(); 初始化窗口对象和 ncurses 代码，返回代表整个屏幕的窗口对象
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* cbreak(); 禁用缓冲并使键入的输入立即可用
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* noecho(); 关闭回显，因此用户输入不会显示在屏幕上
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这些函数定义在 **curses.h** 头文件中，你需要在你的程序中通过以下方式将其包含进来：
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```
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#include <curses.h>
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```
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初始化终端后，你可以自由使用任何 **ncurses** 函数，我们将在示例程序中探讨其中的一些函数。
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当你使用完 **ncurses** 并想返回到常规终端模式下时，使用 **endwin();** 重置一切。此命令可以重置任何屏幕颜色，将光标移动到屏幕的左下角，并使光标可见。通常在退出程序之前执行此操作。
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### 在屏幕上寻址
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关于 **ncurses** 首先需要知道的是屏幕的坐标分为行和列，左上角的是 0,0 点。**ncurses** 定义了两个全局变量来帮助你识别屏幕：LINES 是屏幕的行数，COLS 是屏幕的列数。屏幕右下角的位置是 LINES-1,COLS-1。
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例如，如果你想要移动光标到第 10 行和第 30 列，你可以使用移动函数，移动到此坐标：
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```
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move(10, 30);
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```
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之后显示的任何文本都将从屏幕的该位置开始。要显示单个字符，请对单个字符使用 **addch(c)** 函数。要显示字符串，将对字符串使用 **addstr(s)** 函数。对于类似于 **printf** 的格式化输出，请使用带有常用选项的 **printw(fmt, …)**。
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移动到屏幕指定位置和显示文本是一件很常见的事情，**ncurses** 提供了同时执行这两项操作的快捷方式。**mvaddch(row, col, c)** 函数将在屏幕第 row 行，第 col 列的位置显示一个字符。而 **mvaddstr(row, col, s)** 函数将在屏幕第 row 行，第 col 列的位置显示一个字符串。更直接的例子，在程序中使用 **mvaddstr(10, 30, "Welcome to ncurses");** 函数将从屏幕的第 10 行和第 30 列开始显示文本 "Welcome to ncurses"。使用 **mvaddch(0, 0, '+');** 函数将在屏幕的左上角第 0 行和第 0 列处显示一个加号。
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在终端屏幕上绘制文本会对某些系统产生性能影响，尤其是在较旧的硬件终端上。因此 **ncurses** 允许你“堆叠”一堆文本以显示在屏幕上，然后使用 **refresh()** 函数使所有这些更改对用户可见。
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让我们来看一个将以上所有内容整合在一起的简单示例：
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```
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#include <curses.h>
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int
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main()
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{
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initscr();
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cbreak();
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noecho();
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mvaddch(0, 0, '+');
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mvaddch(LINES - 1, 0, '-');
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mvaddstr(10, 30, "press any key to quit");
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refresh();
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getch();
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endwin();
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}
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```
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程序的开始初始化了一个终端窗口，然后在屏幕的左上角打印了一个加号，在左下角打印了一个减号，在第 10 行和第 30 列打印了 “press any key to quit” 文本。程序通过使用 getch() 函数接收了键盘输入的单个字符，接着，使用 **endwin()** 函数在程序完全退出前重置了终端。
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**getch()** 是一个很有用的函数，你可以使用它来做很多事情。我经常使用它在我退出程序前用来暂停。与大多数 **ncurses** 函数一样，还有一个名为 **mvgetch(row, col)** 的 **getch()** 版本，用于在等待字符输入之前移动到屏幕位置的第 row 行，第 col 列。
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### 使用 ncurses 编译
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如果你尝试以通常的方式编译该示例程序，例如 `gcc pause.c`，你可能会从链接器中获得大量错误列表。那是因为 GNU C 编译器不会自动链接 **ncurses** 库。相反，你需要使用 `-l ncurses` 命令行选项加载它以进行链接。
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```
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$ gcc -o pause pause.c -lncurses
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```
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运行新程序将打印一条简单的 “press any key to quit” 消息，该消息差不多位于屏幕中央：
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![centered message in a program window][2]
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图 1：程序中居中的 “press any key to quit” 消息。
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### 使用 ncurses 构建更好的程序
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探索 **ncurses** 库函数以了解在屏幕上显示文本的其它方法。你可以在 ncurses 的 man 手册页中找到所有 **ncurses** 函数的列表。这给出了 **ncurses** 的一般概述，并提供了不同 **ncurses** 函数的类似表格的列表，并参考了包含完整详细信息的手册页。例如，在 curs_printw(3X) 手册页中描述了 **printw**，您可以通过以下方式查看：
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```
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$ man 3x curs_printw
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```
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更简单点：
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```
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$ man curs_printw
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```
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使用 **ncurses**，你可以创建更多有趣的程序。通过在屏幕上的特定位置打印文本，你可以创建在终端中运行的游戏和高级实用程序。
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--------------------------------------------------------------------------------
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via: https://opensource.com/article/21/8/ncurses-linux
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作者：[Jim Hall][a]
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选题：[lujun9972][b]
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译者：[perfiffer](https://github.com/perfiffer)
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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://opensource.com/users/jim-hall
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[b]: https://github.com/lujun9972
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[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/laptop_screen_desk_work_chat_text.png?itok=UXqIDRDD (Person using a laptop)
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[2]: https://opensource.com/sites/default/files/press-key_0.png
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