how to use StreamReader.Peek() ?

Question

hi: Does anyone can tell me the usage of StreamReader.Peek()? I can not understand the one which written in MSDN.

bamboo3 · Answer

hi nobrainer : I just run your code , I relize that I had a big misunderstanding of the peek() method. thank you for your grate code, now i fully understand it.

bamboo3 · Answer

hi nobrainer : I know that peek() method will not change the position in the stream, that's why I wrote that "The StreamReader.Peek() method returns the ASCII value of the first charactor in THAT Line ." "THAT Line" means the line which peek() method excuted. Sorry that my poor english and the example make you misunderstood ;) and I really appreciate your reply :)

bilnaad · Answer

That's not correct. So I made a little sample for you :) I have a test.txt on my c:\ drive (C:	est.txt) wich has just one line: test.txt ---------------------- 1 This is fun! ---------------------- code --------------------------------------------------- public class Test { /* * test.txt * ----------------- * 1 This is fun! */ static void Main () { StreamReader sr = new StreamReader("C:\test.txt"); Console.WriteLine("-------------------------"); Console.WriteLine("Let's use Peek() 4 times"); Console.WriteLine("-------------------------"); for(int i = 0; i < 4; i++) { int peek = sr.Peek(); Console.WriteLine(string.Format("Peeked at ASCII({0}) char({1})" , peek , Convert.ToChar(peek))); } Console.WriteLine("
-------------------------"); Console.WriteLine("Let's use read() 12 times"); Console.WriteLine(" & "); Console.WriteLine("Let's use Peek() 4 times"); Console.WriteLine("-------------------------"); for(int i = 0; i < 13; i++) { int read = sr.Read(); Console.WriteLine(string.Format("Read at ASCII({0}) char({1})" , read , Convert.ToChar(read))); } for(int i = 0; i < 4; i++) { int peek = sr.Peek(); Console.WriteLine(string.Format("Peeked at ASCII({0}) char({1})" , peek , Convert.ToChar(peek))); } Console.ReadLine(); } } --------------------------------------------------- As you will see when you run this sample that the peek() method returns the value of the NEXT character in the stream. But without consuming the it. This means that the position in the stream stays the same. In your sample you used ReadLine() so the StreamWriter will advance and consume everything untill the next line is reached. So if you use Peek() and ReadLine() simultanious in a loop it will read every first character in the current line. But if you deleted the ReadLine() code from the file you can see it will read the first character in the file over and over. I hope this helps

bamboo3 · Answer

I think I find out the answer. The StreamReader.Peek() method returns the ASCII value of the first charactor in that Line . for example : -----------sample.txt------------- aerdr 0defr 1khki ---------------------------------- -----------Code------------------ // sr is a StreamReader while(sr.Peek() > 1) { Console.WriteLine(sr.Peek().ToString()); Console.WriteLine(sr.ReadLine()); } ------------------------------------------------ -------------result---------------------------- 97 // 97 is the ASCII value of 'a' aerdr 48 // 48 is the ASCII value of '0' 0defr 49 // 49 is the ASCII value of '1' 1khki --------------------------------------------------

bilnaad · Answer

I believe the Peek() method returns the next byte or whatever in the stream but the position on the stream doesn't advance. So you can look if there something interesting up ahead. I hope this helps

how to use StreamReader.Peek() ?

Answers (5)