字符串格式C＃{0,12：N0}（冒号和逗号）的含义是什么？ [英] What is String Format C# {0,12:N0} (colon and commas) means?

问题描述

好的，下面是代码示例：

Okay here's the code example:

 string header = String.Format("{0,-12}{1,8}{2,12}{1,8}{2,12}{3,14}\n",
                                "City", "Year", "Population", "Change (%)");
  Console.WriteLine(header);
  string output;      
  foreach (var city in cities) {
     output = String.Format("{0,-12}{1,8:yyyy}{2,12:N0}{3,8:yyyy}{4,12:N0}{5,14:P1}",
                            city.Item1, city.Item2, city.Item3, city.Item4, city.Item5,
                            (city.Item5 - city.Item3)/ (double)city.Item3);
     Console.WriteLine(output);
  }
 }
}
// The example displays the following output:
//    City            Year  Population    Year  Population    Change (%)
//    
//    Los Angeles     1940   1,504,277    1950   1,970,358        31.0 %
//    New York        1940   7,454,995    1950   7,891,957         5.9 %
//    Chicago         1940   3,396,808    1950   3,620,962         6.6 %
//    Detroit         1940   1,623,452    1950   1,849,568        13.9 %

我理解args {0：N0}表示无小数点后的冒号，但是昏迷呢？像{0，-12}和{1,12}一样，在字符串格式的参数之后逗号是什么意思？

i understand about the colon after the args {0:N0} means no decimal, but what about the comas? like {0,-12}, and {1,12} what does comma means after the argument of the string format?

推荐答案

MSDN文档是您的朋友（我在上面的评论中给出的链接也不是最好的）：

复合格式

MSDN Documentation is your friend (the link I gave in comments above wasn't the best either):
Composite Formatting

每个格式项都需要格式，由以下部分组成：
{index [，alignment] [：formatString]}

Each format item takes the following form and consists of the following components: {index[,alignment][:formatString]}

因此 index 显然是所提供参数的索引：

So the index is obviously the index of the provided arguments:

String.Format("Second argument = {1}, first argument = {0}", arg1, arg2);

对齐方式指定所需的字段宽度和水平对齐方式：

Alignment specifies the desired width of the field and horizontal alignment:

如果对齐方式为正，则字段中的格式化数据为右对齐，如果对齐方式为负，则为左对齐。 / p>

The formatted data in the field is right-aligned if alignment is positive and left-aligned if alignment is negative.

String.Format("{0,-12}" +    // first argument, left align, 12 character wide column
              "{1,8:yyyy}" + // second argument, right align, 8 character wide column,
                             // formatted as a year
              "{2,12:N0}" +  // third argument, right align, 12 character wide column,
                             // formatted as a number, 0 decimal places

和您已经知道的 formatString （例如数字（ N）格式说明符）。

And formatString you already know about (e.g. The Numeric ("N") Format Specifier).

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