How to open Explorer with a specific file selected?

To follow up on @Mahmoud Al-Qudsi's answer. when he says "launching the process", this is what worked for me:

// assume variable "path" has the full path to the file, but possibly with / delimiters
for ( int i = 0 ; path[ i ] != 0 ; i++ )
{
    if ( path[ i ] == '/' )
    {
        path[ i ] = '\\';
    }
}
std::string s = "explorer.exe /select,\"";
s += path;
s += "\"";
PROCESS_INFORMATION processInformation;
STARTUPINFOA startupInfo;
ZeroMemory( &startupInfo, sizeof(startupInfo) );
startupInfo.cb = sizeof( STARTUPINFOA );
ZeroMemory( &processInformation, sizeof( processInformation ) );
CreateProcessA( NULL, (LPSTR)s.c_str(), NULL, NULL, FALSE, 0, NULL, NULL, &startupInfo, &processInformation );

The supported method since Windows XP (i.e. not supported on Windows 2000 or earlier) is SHOpenFolderAndSelectItems:

void OpenFolderAndSelectItem(String filename)
{
   // Parse the full filename into a pidl
   PIDLIST_ABSOLUTE pidl;
   SFGAO flags;
   SHParseDisplayName(filename, null, out pidl, 0, out flags);
   try 
   {
      // Open Explorer and select the thing
      SHOpenFolderAndSelectItems(pidl, 0, null, 0);
   }
   finally 
   {
      // Use the task allocator to free to returned pidl
      CoTaskMemFree(pidl);
   }
}

Easiest way without using Win32 shell functions is to simply launch explorer.exe with the /select parameter. For example, launching the process

explorer.exe /select,"C:\Folder\subfolder\file.txt"

will open a new explorer window to C:\Folder\subfolder with file.txt selected.

If you wish to do it programmatically without launching a new process, you'll need to use the shell function SHOpenFolderAndSelectItems, which is what the /select command to explorer.exe will use internally. Note that this requires the use of PIDLs, and can be a real PITA if you are not familiar with how the shell APIs work.

Here's a complete, programmatic implementation of the /select approach, with path cleanup thanks to suggestions from @Bhushan and @tehDorf:

public bool ExploreFile(string filePath) {
    if (!System.IO.File.Exists(filePath)) {
        return false;
    }
    //Clean up file path so it can be navigated OK
    filePath = System.IO.Path.GetFullPath(filePath);
    System.Diagnostics.Process.Start("explorer.exe", string.Format("/select,\"{0}\"", filePath));
    return true;
}

Reference: Explorer.exe Command-line switches