Using a string builder, i've read a file.. How do i find if the given string is present in the file or not?

问题

I've read a file into StringBuilder. When I give a string as an input, if the word is present in the file, the output should be true.. If its not present, it should be false.. How do i do it? Could someone help me with the code? I've written the program till here.. How do i go further? Thanks alot.. :)

class Program
{
    static void Main(string[] args)
    {
        using (StreamReader Reader = new StreamReader("C://myfile2.txt"))
        {
            StringBuilder Sb = new StringBuilder();
            Sb.Append(Reader.ReadToEnd());
            {
                Console.WriteLine("The File is read");   
            }
        }
    }
}

回答1:

using (System.IO.StreamReader Reader = new System.IO.StreamReader("C://myfile2.txt"))
{
      string fileContent = Reader.ReadToEnd();
       if (fileContent.Contains("your search text"))
           return true;
       else
           return false;
}

回答2:

How about an one-liner:

 bool textExists = System.IO.File.ReadAllText("C:\\myfile2.txt").Contains("Search text");

That should do the trick :)

回答3:

In the example you show - there is no point loading into a StringBuilder in the first place. You already return the entire string in the call to StreamReader.ReadToEnd, so you may as well just check if this contains your substring.

StringBuilder is very useful if you are changing and mutating the string - but in this use case, you are not.

How about this:

private bool FileContainsString(string file, string substring)
{
    using (StreamReader reader = new StreamReader("C://myfile2.txt"))
    {
        return reader.ReadToEnd().Contains(substring);
    }
}

If you definitely want the string builder, then something like this:

private bool FileContainsString(string file, string substring)
{
    using (StreamReader reader = new StreamReader("C://myfile2.txt"))
    {
        var sb = new StringBuilder(reader.ReadToEnd());
        return sb.ToString().Contains(substring);
    }
}

but in this specific scenario the StringBuilder is not actually doing anything useful.

回答4:

You can read the whole file into a string with File.ReadAllText. Note that this does load the whole file at once, and thus costs a lot of memory if the file is large:

string content = File.ReadAllText(@"C:\myfile2.txt");
Console.WriteLine(content.Contains("needle"));

---

If your needle doesn't span multiple lines you can go with:

IEnumerable<string> content = File.ReadLines(@"C:\myfile2.txt");
Console.WriteLine(content.Any(line => line.Contains("needle")));

This only needs to keep one line in memory at a time, and thus scaled to larger files.

回答5:

Assign that to a string and then check if it contains the substring.

dim str as string
str = sb.tostring()
if str.contains("string") then
 'code
else
 'code
end if

来源：https://stackoverflow.com/questions/9785650/using-a-string-builder-ive-read-a-file-how-do-i-find-if-the-given-string-is