c - 需要有关在 printf 转换规范中设置字段宽度的指示

Question

这是一个非常基本的事情，但我需要有关如何设置字段宽度的指导，以便表格对于所有允许的值都可以很好且整齐地打印出来。我已经玩了一段时间并且遇到了麻烦。是否有一些技巧可以快速弄清楚？只要朝着正确的方向插入，我们将不胜感激。

 //Print the results in a table
printf("\n#============================================#\n");
printf("| Description                 |  Input Data  |\n");
printf("|============================================|\n");
printf("| Loan amount                 | $  %8.2f  |\n", loan);
printf("| Yearly interest rate        |      %6.2f% |\n", rate);
printf("| Number of years             |       %d     |\n", years);
printf("|============================================|\n");
printf("| Payment Details             |   Results    |\n");
printf("|============================================|\n");
printf("| The monthly payment will be | $     %5.2f  |\n", monthlyPayment);
printf("| Interest paid               | $    %6.2f  |\n", interestEarned);
printf("#============================================#\n\n");

Answer 1

格式化数据更接近艺术而不是科学。

1. 考虑到字段宽度会在项目的生命周期中发生变化(更有可能增长)。

2. 发布代码以便于维护。第一次永远不会正确。性能并不那么重要，因为输出无论如何都是 CPU 周期的一个坑。

3. 重复使用格式。

4. 避免使用字符串文字的 fprintf()，而是使用 fputs()。

5. fprintf() 上的 RTFM，让最小宽度说明符成为您的 friend 。

6. 注意格式中的单独“%”。应为"%%"

第一次尝试:

  double loan, rate,  monthlyPayment, interestEarned;
  loan = interestEarned = monthlyPayment = 12345.78;
  rate = 999.99;
  int years = 30;

  //  Let us assume interesting part of the table is 10 wide

  // 10 =
  // .max_width
  const char *fdash = "%s%.10s%s";

  // space, 8 char, space
  // - left justify
  // min_width.max_width
  const char *ftext = "%s %-8.8s %s";

  // $, 8 width with 2 dec. places, space
  // width.precision
  const char *fcash = "%s$%8.2f %s";

  // space, 7 width, %, space  
  // width.precision
  const char *fperc = "%s %7.2f%% %s";

  // space, 8 wide, space
  // width
  const char *fyear = "%s %8d %s";
  const char *bar   = "=================================="; // extra long

  fputs("\n", stdout);
  printf(fdash, "#==============================", bar           , "#\n");
  printf(ftext, "| Description                 |", "Input Data"  , "|\n");
  printf(fdash, "|==============================", bar           , "|\n");
  printf(fcash, "| Loan amount                 |", loan          , "|\n");
  printf(fperc, "| Yearly interest rate        |", rate          , "|\n");
  printf(fyear, "| Number of years             |", years         , "|\n");
  printf(fdash, "|==============================", bar           , "|\n");
  printf(ftext, "| Payment Details             |", "Results"     , "|\n");
  printf(fdash, "|==============================", bar           , "|\n");
  printf(fcash, "| The monthly payment will be |", monthlyPayment, "|\n");
  printf(fcash, "| Interest paid               |", interestEarned, "|\n");
  printf(fdash, "#==============================", bar           , "#\n");
  fputs("\n", stdout);

输出:对于“输入数据”来说字段太小。为用户修复左侧。

#========================================#
| Description                 | Input Da |
|========================================|
| Loan amount                 |$12345.78 |
| Yearly interest rate        |  999.99% |
| Number of years             |       30 |
|========================================|
| Payment Details             | Results  |
|========================================|
| The monthly payment will be |$12345.78 |
| Interest paid               |$12345.78 |
#========================================#