c - 如何在C中对文本中的 float 进行四舍五入？

Question

所以我有这段文字

today average human lifespan in Western countries is approaching and exceeding 80 years.
1 Japan 82.6 123 19
2 Hong Kong 82.2 234 411
3 Iceland 81.8 345 26
4 Switzerland 81.7 456 7
5 Australia 81.2 567 500
...
80 Lithuania 73.0 800 2
...
194 Swaziland 39.6 142 212
195 133714 18.0 133 998
196 100110011 10.0 667 87351

我需要将本文中的 float 四舍五入为整数。我搜索了很多论坛，但似乎找不到我需要的东西。该文本在 .txt 文件中给出。我的任务:“将实数(有小数)四舍五入为整数。更正后的文本应该位于新的 .txt 中”就是这样。

Answer 1

scanf 和 sscanf 是提取字符串中任何内容的最佳 friend 。
floor 使用 full 来抑制浮点上的小数。然后可以用来对其进行舍入(使用它包括 math.h)...

格式字符串描述了预期的格式。函数返回找到的参数数量。

示例:

• 初始化

  int id = -1;
  char country[160]; /* /!\ Warning country name length shall be fewer than 160 */
                     /*      Scanf don't care of this array parameter length. If it is too short */
                     /*      It will erase following memory...                 */
                     /* That is why scanf are often disparaging                   */
  float percent = 0.0;
  char a_number_as_string[10];
  int other_number = -1;
  char* Switzerland = "4 Switzerland 81.7654321 456 7";
  

• 效果代码

   int ret = sscanf(Switzerland, "%d %s %f %s %d", &id, country, 
                    &percent, a_number_as_string, &other_number);
   if(ret == 5) {
       printf("~~ id: %d\n\tcountry: %s\n\tpercent: %.2f\n\tand    : "
              "(%s, %d)\n", id, country, percent, a_number_as_string,
              other_number);
  
       /////// ROUND
       printf("*** round");
       printf("\twith printf %%.1f = %.1f\n", percent);
       printf("\twith printf %%.2f = %.2f\n", percent);
       printf("\twith printf %%.3f = %.3f\n", percent);
       printf("\twith printf %%.4f = %.4f\n", percent);
  
       printf("*** With floor (included in math.h)\n");
       printf("\t1 decimal: %f\n", floor(percent*10)/10);
       printf("\t2 decimal: %f\n", floor(percent*100)/100);
       printf("\t3 decimal: %f\n", floor(percent*1000)/1000);
       printf("\t4 decimal: %f\n", floor(percent*10000)/10000);
   } else {
       printf("--> ret = %d", ret);
   }
  

• 输出

  ~~ id: 4

  country: Switzerland
  percent: 81.70
  and : (456, 7)

  *** 圆形

  with printf %.1f = 81.8
  with printf %.2f = 81.77
  with printf %.3f = 81.765
  with printf %.4f = 81.7654

  *** 有底线(包含在 math.h 中)

  1 decimal: 81.700000
  2 decimal: 81.760000
  3 decimal: 81.765000
  4 decimal: 81.765400

此函数在 Unix、OSX、Unix 终端手册页中进行了描述:

• man scanf
• man sscanf
• 男人楼层

或者您可以在网络上管理此管理器的多个副本中找到它，例如

• scanf
• sscanf
• floor