Reading and Writing Text to Files - Page 4

In the previous page you learned how to write files, and I began talking about how to check if a file exists. In this page, I'll continue from where we left off and talk more about checking whether files exist.

Something to remember is that a file is created or overwritten when your StreamWriter is initialized with the path to your file. Therefore, something like the following will not work like you would want to:

string filePath = "C:\\Users\\Kirupa\\Desktop\\foo.txt";

 

StreamWriter foo = new StreamWriter(filePath);

 

if (File.Exists(filePath))

{

// File exists

}

else

{

// File does not exist

}

The reason is that the moment your StreamWriter object foo is initialized, the file pointing to by filePath will be created or overwritten. Our File.Exists boolean will always return true because no matter what you reasonably do, a file at filePath will exist.

If you want to avoid overwriting an existing file, the following approach works better:

string filePath = "C:\\Users\\Kirupa\\Desktop\\foo.txt";

 

StreamWriter foo;

 

if (File.Exists(filePath))

{

// File exists

// Don't do anything.

}

else

{

// File does not exist

foo = new StreamWriter(filePath);

foo.Write("Blarg. Zorb. Zeeb. Foo.");

foo.Close();

}

In the above code, a file is created only if File.Exists returns false. Notice that our StreamWriter object foo isn't being initialized until our code reaches the File.Exists == false condition.

Asynchronous File Handling
Both the StreamReader and StreamWriter classes work asynchronously. That's a cool sounding word that basically means that you can do other things when using StreamReader or StreamWriter. To take a real world example, if you were opening a huge text file, you can continue to use your application and everything will seem to work fine without suffering delays or lags associated with reading your file.

If both of those classes were not asynchronous, then you would have to use Threads to ensure any time consuming reading or writing task operates semi-independently from other tasks. Threads is an interesting topic that I will save for a later article.

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