I kept the faith knowing that [the detailed instructions](https://sqlite.org/forum/forumpost/e89f92050564a2d8?t=h) would have been tested successfully and persevered. Several hours later I have created FILEIO.DLL <code> 20/09/2021 14:43 148,992 fileio.dll </code> <i>Larry, I'd be interested to know how the size compares with the size of your FILEIO.DLL.</i> I have tested this extension and no longer get the [aberration I reported](https://sqlite.org/forum/forumpost/8314c494ec1ec7fa?t=h) The steps I followed are: <b>Step 1</b> Start Command Prompt as Administrator <b>Step 2</b> Find the location of CL.EXE; the location should have the dependencies mspd*.DLL. In my case, this location is: <i>cd "D:\\Program Files (x86)\\Microsoft Visual Studio\\2019\\Enterprise\\VC\\Tools\\MSVC\14.29.30133\\bin\\Hostx86\\x86"</i> That is, I have to be in this directory. <b>Step 3</b> Find the batch file that creates the environment wherein CL.EXE can find the *.h dependencies. In my case this batch file is: <i>"D:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Auxiliary\Build\vcvars32.bat" </i> I ran this batch file which provided this response: <code> [vcvarsall.bat] Environment initialized for: 'x86' </code> <b>Step 4</b> > cl -Os "E:\SQLite_The Hospital\FILEIO\utf8_to_wide.c" -link -dll -out:fileio.dll This provided this feedback: <code> Microsoft (R) C/C++ Optimizing Compiler Version 19.29.30133 for x86 Copyright (C) Microsoft Corporation. All rights reserved. utf8_to_wide.c Microsoft (R) Incremental Linker Version 14.29.30133.0 Copyright (C) Microsoft Corporation. All rights reserved. /out:utf8_to_wide.exe -dll -out:fileio.dll utf8_to_wide.obj Creating library fileio.lib and object fileio.exp </code> <b>Step 5</b> Since <i>"D:\\Program Files (x86)\\Microsoft Visual Studio\\2019\Enterprise\\VC\\Tools\\MSVC\\14.29.30133\\bin\\Hostx86\\x86"</i> is a system location (<i>the reason for running as Administrator</i>) , I need to tidy up. - Deleted utf8_to_wide.obj - Copied FILEIO.DLL to another (preferred) location - Deleted FILEIO.* <b>Step 6</b> Tested FILEIO.DLL from my preferred location with success. Hopefully, this experience will save me (& others) time when compiling other extensions. <span style="color:red"><b>Larry, thank you very much.</b></span>.