使用正则表达式在文件中查找日期字符串

Question

I need to find a specific date string in a text file. There currently are two date strings in the file - "Due Date: 01/26/2016" and "Date: 01/252016". I need to find the second one but my current code only finds the first one. I am guessing regex would be a better implementation but not sure how to code for it.

Current code -

searchString = "Date:";
if (fileContents.IndexOf(searchString) > 0)
{
    string tmp = fileContents.Substring(fileContents.IndexOf(searchString) + searchString.Length).Trim();
    string loan_date = tmp.Substring(0, tmp.IndexOf('\r')).Trim();
    if (loan_date.Count(x => x == '/') == 1)
    {
        StringBuilder sb = new StringBuilder(loan_date);
        sb[sb.Length - 4] = '/';
        loan_date = sb.ToString();
    }
    DateTime dt = DateTime.ParseExact(loan_date, "M/d/yyyy", System.Globalization.CultureInfo.InvariantCulture);
    return dt;
}

Answer 1

In C#, you can find matches to a regex by doing something like the following.

using System;
using System.Text.RegularExpressions;

public class Example
{
    public static void Main()
    {
        string pattern = "[0-1]?[0-9]/[0-9]{2}/[0-9]{4}";
        string input = "Due Date: 01/26/2016 Date: 01/25/2016";

        foreach (var m in Regex.Matches(input, pattern)) {
            Console.WriteLine("'{0}' found at index {1}.", 
                       m.Value, m.Index);
        }
    }
}

That regex specifically means 0 or 1 (optional) followed by a digit, followed by a slash, followed by two digits, followed by a slash, followed by four digits.

I'm also assuming your second date 01/252016 contains a typo.

Answer 2

Try this Regex:

(Due\s)?(Date:)\s([0-1][0-2])\/([0-3][0-9])\/([0-2][0-9]{3})

Since both strings include "Date", we can use that to further filter out other strings (you might not actually want all dates). Since Due is optional, we can mark it as so. It's a little tough to filter out poorly formatted dates, but you can limit a few things (like I have above). You will have to validate the date separately just to be sure.

Here is a Regex that will not care about the checks as long as it's formatted correctly:

(Due\s)?(Date:)\s([0-9]{2})\/([0-9]{2})\/([0-9]{4})

Or just the dates:

([0-9]{2})\/([0-9]{2})\/([0-9]{4})