SDL_Log and the other logging functions use WriteConsole() on Windows to print the log messages, but that only works if the output is an actual windows console (see https://docs.microsoft.com/en-us/windows/console/writeconsole).

For example if I run my application using something like:
 myapp.exe > output.txt 2>&1

that would redirect both the stdout and stderr to a file -> the calls to SDL_Log just fail. I have the same problem when running the application from the CLion IDE. I don't know how it handles the console but all calls to WriteConsole fail.

I made a patch that detects when the output handle is not a console (as mentioned in the above link) and uses WriteFile then instead. That seems to fix both the problems I was having.

As a side note: the indentation in SDL_log.c was a bit all over the place, but I didn't touch it to make it clearer what was changed.