c# - 如果用同一个val来替换两个单独的string.Format占位符，一定要提供两次吗？

Question

鉴于这种：

string msg = string.Format("Duckbill {0} Platypus has not been loaded. Fetch Duckbill {1}'s Platypus then continue.", userDuckbill, userDuckbill);

...改为这样做就足够了：

string msg = string.Format("Duckbill {0} Platypus has not been loaded. Fetch Duckbill {1}'s Platypus then continue.", userDuckbill);

?

Answer 1

您可以多次指定参数。改用这个：

string msg = string.Format("Duckbill {0} Platypus has not been loaded. Fetch Duckbill {0}'s Platypus then continue.", userDuckbill);

官方文档有几个这样的例子。这里只有一个：

  string formatString = "    {0,10} ({0,8:X8})\n" + 
                        "And {1,10} ({1,8:X8})\n" + 
                        "  = {2,10} ({2,8:X8})";
  int value1 = 16932;
  int value2 = 15421;
  string result = String.Format(formatString, value1, value2, value1 & value2);

Answer 2

使用{0}两次：

string msg = string.Format(
    "Duckbill {0} Platypus has not been loaded. Fetch Duckbill {0}'s Platypus then continue.",
    userDuckbill);

您的第二个代码示例将产生FormatException以下消息：

索引（从零开始）必须大于或等于零且小于参数列表的大小。

因此，无论何时使用，格式字符串后{n}都必须至少有参数。n然而，拥有更多n是无用的。