如何获取字符串中第二个逗号的索引？C#字符串截取异常问题解决

Hey there! Let's break down your two questions and fix that CSV parsing issue:

1. How to get the index of the second comma in a string? #

To find the second comma, use the overloaded version of IndexOf that lets you specify a starting position for the search. Here's the straightforward approach:

• First, grab the index of the first comma with string.IndexOf(',')
• Then, start searching from the position right after the first comma (firstComma + 1) to locate the second comma:

  int firstComma = csvString.IndexOf(',');
  int secondComma = csvString.IndexOf(',', firstComma + 1);
  

For example, in the string "5,M,true", the first comma sits at index 1. Starting the search at index 2 finds the second comma at index 3.

2. Fixing the Block Letter extraction issue #

The problem in your original code stems from a common misunderstanding of C#'s Substring method: the second parameter is the length of the substring to take, not the ending index.

Your original line:

string blockLetter = csvString.Substring(firstComma + 1, secondComma);

In the input "5,M,true", firstComma + 1 equals 2, and secondComma equals 3. This tells Substring to take 3 characters starting at index 2, which gives you "M,t" instead of just "M".

Your corrected solution is spot-on! #

You already fixed this by explicitly taking 1 character after the first comma—perfect for your use case since you want a single char:

char blockLetter = char.Parse(csvString.Substring(firstComma + 1, 1));

If you ever need to handle longer values between commas (though you noted you want a char), you could calculate the exact length between the two commas like this:

string blockLetter = csvString.Substring(firstComma + 1, secondComma - (firstComma + 1));

Here's your full corrected code: #

//read
Console.Write("Please enter (pyramid slot number,block letter,whether or not the block should be lit): ");
string csvString = Console.ReadLine();
//location of comma
int firstComma = csvString.IndexOf(',');
int secondComma = csvString.IndexOf(',', firstComma + 1);
//extract slot number of pyramid
int slotNumber = int.Parse(csvString.Substring(0, firstComma));
// Corrected: directly parse the single character after first comma
char blockLetter = char.Parse(csvString.Substring(firstComma + 1, 1));
bool lit = bool.Parse(csvString.Substring(secondComma + 1));
//print
Console.WriteLine("Pyramid Slot Number: " + slotNumber);
Console.WriteLine("Block Letter: " + blockLetter);
Console.WriteLine("Lit: " + lit);

内容的提问来源于stack exchange，提问作者MetroRN