Question

Say you have a text file – what’s the fastest and/or most memory efficient way to determine the number of lines of text in that file?

Is it simply a matter of scanning through it character by character and looking for newline characters?

Answer 1

Probably not the fastest but it will be the most versatile…

int lines = 0;
/* if you need to use an encoding other than UTF-8 you way want to try...
   new StreamReader("filename.txt", yourEncoding) 
   ... instead of File.OpenText("myFile.txt")
*/
using (var fs = File.OpenText("myFile.txt"))
    while (!fs.EndOfStream)
    {
        fs.ReadLine();
        lines++;
    }

… this will probably be faster …

if you need even more speed you might try a Duff’s device and check 10 or 20 bytes before the branch

int lines = 0;
var buffer = new byte[32768];
var bufferLen = 1;    
using (var fs = File.OpenRead("filename.txt"))
    while (bufferLen > 0)
    {
        bufferLen = fs.Read(buffer, 0, 32768);
        for (int i = 0; i < bufferLen; i++)
            /* this is only known to work for UTF-8/ASCII other 
               file types may need to search for different End Of Line 
               characters */                
            if (buffer[i] == 10)           
                lines++;
    }