Reading Text Files

File.ReadLines

more efficient than using ReadAllLines for large files.
Returns an IEnumerable<string> of all the lines of code.

IEnumerable<string> enumLines; 
string[] lines; 

enumLines = System.IO.File.ReadLines(@"C:\\temp\\myfile.txt", Encoding.UTF8); 

lines = enumLines.ToArray();

foreach (string line in lines) 
{ 
} 

File.ReadAllLines

Added in .NET 4.0
Reads each line into a string array.

string[] lines; 
lines = System.IO.File.ReadAllLines(@"C:\\temp\\myfile.txt"); 
foreach (string line in lines) 
{ 
} 

Reads each line into a collection

System.Collections.Generic.List<string> myList; 
myList = System.IO.File.ReadAllLines("C:\temp\SavedLists.txt"); 

File.ReadAllText

Should only be used on very small, basic files

string sWholeFile; 
string[] lines; 

sWholeFile = System.IO.File.ReadAllText(@"C:\\temp\\myfile.txt"); 
lines = sWholeFile.Split(Environment.NewLine); 

StreamReader.ReadToEnd

System.IO.StreamReader oStreamReader; 
string sWholeFile; 

oStreamReader = System.IO.StreamReader(@"C:\\temp\\myfile.txt"); 
sWholeFile = oStreamReader.ReadToEnd; 

StreamReader.ReadToEndAsync

System.IO.StreamReader oStreamReader; 
string sWholeFile; 

oStreamReader = System.IO.StreamReader(@"C:\\temp\\myfile.txt"); 
using (oStreamReader) 
{ 
   sWholeFile = await oStreamReader.ReadToEndAsync(); 
} 

StreamReader.ReadLine

Reads each line into a string array.

System.IO.StreamReader oStreamReader; 
string sWholeFile; 

oStreamReader = System.IO.StreamReader(@"C:\\temp\\myfile.txt"); 
while ( (line = oStreamReader.ReadLine() ) != null) 
{ 
}