如何使用填充正确格式化 printf()? [英] How to format printf() correctly with padding?

问题描述

我正在重新创建 unix shell 命令，目前正在执行 ls.我必须模仿 ls -l 来显示权限、文件大小等.本机 ls -l 如果格式正确，则每一列都保持对齐，如下所示:

I am re-creating the unix shell commands and am currently doing ls. I have to mimic ls -l which shows permissions, file size, ect. The native ls -l if formatted well so every column stays aligned like this:

-rw-r--r-- 1 matt matt 1474560 Apr 11 14:54 diskimage
drwxr-xr-x 2 matt matt    4096 Mar 25 15:31 Example
-rwxr-xr-x 1 matt matt   26375 Apr 12 14:24 final
-rwxr-xr-x 1 matt matt      75 Apr 11 14:39 log.sh

现在，我的 ls 版本做了几乎相同的事情，除了当 printf() 函数中使用不同的值时我的列不会对齐，如下所示:

Right now, my version of ls does almost the same thing, except my columns do not line up when different values are used in the printf() function like this:

drwxr-xr-x     0   1024    Dec 03 14:11      .
drwxr-xr-x     0   1024    Dec 03 14:11      ..
drwxr-xr-x     0   1024    Dec 03 13:57      Z
drwxr-xr-x     0   1024    Dec 03 14:11      X
drwxr-xr-x     0   1024    Dec 03 13:56      Y
-rw-r--r--     0   334632    Dec 10 08:39      big

如您所见，最后一个条目未对齐，因为大小列比其余条目大.如何告诉 printf 函数以自动对齐列的格式化方式打印?

As you can see, the last entry is not aligned because the size column is bigger than the rest. How can I tell the printf function to print in a formatted way with automatically aligned columns?

推荐答案

方法如下:

printf("%8d", 334632);

d 转换说明符之前的数字告诉 printf() 用空格填充打印的数字，以便它(至少)在屏幕上占据(至少)8 个字符.你可以在那里写任何整数.您案例的完整格式字符串可能类似于:

The number before the d conversion specifier tells printf() to pad the printed number with whitespace so that it occupies (at least) for example, 8 characters on screen. You can write any integer number there. A complete format string for your case might be something like:

"%9s\t%4d\t%8d\t%16s\n"

如果您想要可变数量的填充:

If you want a variable amount of padding:

printf("%*d\n", max_field_width, 42);

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