I presume you want to write from another program. You can call a command line shell (done via the "system()" command under C) which then calls the elog executable. If you absolutely want a DLL, you can einter try to compile one yourself using the fuctions in elog.c, or use the curl DLL with which you can also submit elog entries. See elog:68597 for usage of curl. While curl is usually executed from the command line, there is also a curl library containing the same functionality. See https://curl.haxx.se/windows/