Working with the System.IO.Directory Class in C#

Introduction

This article is focused on understanding the Directory class of System.IO namespace. The Directory class exposes routines for manipulating directories & subdirectories. It contains all kinds of routines like creating, moving, and enumerating through directories and subdirectories. In most of the application developments we require some file accesses or directory accesses normally we use some low-level system API like Directory-Control Routines in C (eg. _mkdir, _chdir, _rmdir) or Platform SDK function of Kernel32.lib (eg. CreateDirectory,SetCurrentDirectory,RemoveDirectory). In .net we have System.IO.Directory class to do all directory manipulation. For better understanding I will compare code with some C & SDK programs. You will see how easy it is in C# when compared to old programming languages.

Let take a small example to get all the available drive information (this includes both physical & logical drives).

Using C routines

#include <stdio.h>
#include <conio.h>
#include <direct.h>
#include <stdlib.h>
#include <ctype.h>
void main( void ){ 
  int drive, curdrive;
  static char path[_MAX_PATH]; 
  /* Save current drive. */
  curdrive = _getdrive(); 
  printf( "Using C API, Available drives are: \n");
  /* If we can switch to the drive, it exists. */
  for( drive = 1; drive <= 26; drive++ ) 
    if( !_chdrive( drive ) )
       printf( "%c: \n", drive + 'A' - 1 );
}

 Output:
Using C API, Available drives are:
A:\
C:\
D:\
E:\
Z:\

Using Platform SDK File I/O routines

#include <Windows.h>
#include <stdio.h>
void main( void )
{
  char *lpBuffer=new char[1000];
  long retSize;
  retSize=GetLogicalDriveStrings(1000,lpBuffer);
  printf("Using SDK API, Available drives are:");
  for(int i=0;i<=retSize;i++)
  {
    if(lpBuffer[i]!='0')
      printf("%c",lpBuffer[i]);
    else
      printf("");
  }
}

  Output:
Using SDK API, Available drives are:
A:\
C:\
D:\
E:\
Z:\

The same program we will do in C#

getDr.cs

using System; 
using System.IO;
class getDr
{
    public static void Main()
    {
        try
        {

            string[] str=Directory.GetLogicalDrives();
            Console.WriteLine( "Using C# Directory Class,Available drives are:");
            for(int i=0;i< str.Length;i++)
                Console.WriteLine(str[i]);
        }
        catch(IOException e) { Console.WriteLine(e.ToString()); }

    } // end of Main

}//end of Class

So lets understand how this works System.IO.Directory class has method called GetLogicalDrives this method returns all available drives in your system as array of strings. Before that some important thing to remember is all methods of the Directory class are static and can therefore be called without having an instance of a directory. The static methods of the Directory class do a security check on all methods. If you are going to reuse an object several times, consider using the corresponding instance method of DirectoryInfo instead, because the security check will not always be necessary.

Now that we know about Directory class so we will examine the IL code of C# sample (getDr.exe) and also System.IO library.

// IL code of sample code getDr.exe)
IL_0000:call string[] ['mscorlib']'System.IO'.'Directory'::'GetLogicalDrives'()


//IL code of System.IO library)
IL_000b:  call  int32 Microsoft.Win32.Win32Native::GetLogicalDrives()


//IL code of System.IO library)
.method assembly hidebysig static pinvokeimpl("kernel32.dll" lasterr winapi) 
        int32  GetLogicalDrives() cil managed preservesig
{ }

If you see the above IL code of System.IO library it internally calls the kernel32.dll GetLogicalDrives which is nothing but File I/O function in Kernel32.dll library which retrieves a bitmask representing the currently available disk drives. When you call Directory Class methods of System.IO library it internally PInvokes the Microsoft Win32 native functions (see the above Platform SDK code).

Similarly we will see a sample code to create and change directory. For this sample code we will be using Directory.CreateDirectory, Directory.GetCurrentDirectory, Directory.Delete, Directory.Exists and Directory.SetCurrentDirectory.

chgDr.cs

using System;
using System.IO;
class chgDr
{
    public static void Main()
    {
        try
        {
            Console.WriteLine("-->Your Current Directory");
            String curDir=Directory.GetCurrentDirectory();
            Console.WriteLine(curDir);
            String newDir="TestDir";
            Directory.CreateDirectory(newDir);
            Console.WriteLine("--> '" + newDir + "' Directory created");
            Directory.SetCurrentDirectory(newDir);
            Console.WriteLine("--> Changing to '" + newDir + 
                              "'  Directory ");
            Console.WriteLine(Directory.GetCurrentDirectory());
            Console.WriteLine("--> Changing to '" + 
                              curDir + "' Directory ");
            Directory.SetCurrentDirectory(curDir);
            Console.WriteLine(Directory.GetCurrentDirectory());
            Console.WriteLine("--> Deleting  '" + newDir + "' Directory ");
            if(Directory.Exists(newDir))
                Directory.Delete(newDir);
            Console.WriteLine("--> Checking  '" + newDir + 
                              "' Directory Exists or not");

            if(!Directory.Exists(newDir))
                Console.WriteLine("'" + newDir + "' Does not exists ");
        }
        catch(IOException e){ Console.WriteLine(e.ToString()); }
    }

}

Output:
D:\samples\vstudio>chgDr
-->Your Current Directory
D:\samples\vstudio
--> 'TestDir' Directory created
--> Changing to 'TestDir'  Directory
D:\samples\vstudio\TestDir
--> Changing to 'D:\samples\vstudio' Directory
D:\samples\vstudio
--> Deleting  'TestDir' Directory
--> Checking  'TestDir' Directory Exists or not
'TestDir' Does not exists

Some points to remember:

1. Path names are limited to 248 characters

2. The specified path can also refer to a relative path or a Universal Naming Convention (UNC) path for server and share name.

3. Ensure that your paths are well-formed when using methods that accept a path string. In C#, path names should have \\ instead of singe \

4. If you don’t have permission it will generate FileIOPermission exception.

Further reading

1. .NET More information on .NET technologies.

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