Link Error LNK2001: Unresolved External Symbol _mainthread

To avoid these unresolved external errors, do not set the Project Settings to Single-Threaded for an MFC version 3.0 or later application. This setting can be changed by doing the following:

• On Microsoft Visual C++ .NET 2003
  1. Click the Project menu.
  2. Click <project_name> Properties.
  3. Expand Configuration Properties, and then click C/C++.
  4. Click Code Generation.
  5. In the right pane, make a selection other than Single-threaded or Single-threaded Debug in the Runtime Library list.
• On Microsoft Visual C ++ 2.x, 5.0, and 6.0
  1. Select the Project menu.
  2. Select the Settings... option.
  3. Select the C/C++ tab.
  4. Select Code Generation on the Category list box.
  5. Finally, make a selection other than Single-Threaded on the Use Run Time Library list box.
• On Microsoft Visual C++ 4.x
  1. Select the Build menu.
  2. Select the Settings... option.
  3. Select the C/C++ tab.
  4. Select Code Generation on the Category list box.
  5. Finally, make a selection other than Single-Threaded on the Use Run Time Library list box.

Note In Visual Studio 2005 and in later versions, single-threaded CRT is no longer available. For more information, visit the following MSDN Web sites:

C run-time libraries