Make String concatenation faster in C# [duplicate]

Answer 1

When you read a file byte by byte, it can take too long. I would recommend that you read a block of bytes (for example 1024 or 2048) in the loop. Then, in the block you have read, use a regular expression to match your character, particularly if you have a extremely large file.

Sample code would be something like this:

private string GetFileData(string fileName, string matchChar)
{
    StringBuilder x = new StringBuilder();
    int blockCount = 2048;
    int offset = 0;
    string pattern = matchChar;
    int k = -1;
    using (var sr = new System.IO.FileStream(fileName, System.IO.FileMode.Open))
    {
       while ((sr.CanRead) && (k != 0))
       {
           byte[] bt = new byte[blockCount];
           k = sr.Read(bt, 0, blockCount);
           string so = System.Text.UTF8Encoding.UTF8.GetString(bt);
           var m = new System.Text.RegularExpressions.Regex(pattern).Matches(so);
           foreach (System.Text.RegularExpressions.Match item in m)
           {
               x.Append(item.Value);
           }
       }
    }
    return x.ToString();
}

You would call this as

GetFileData(@"c:\matchtest.ono", "a");