If a standard I/O stream is set to SDL_PROCESS_STDIO_INHERITED, it will go to the same place as the
application's I/O stream. This is the default for standard output and standard error.
If a standard I/O stream is set to SDL_PROCESS_STDIO_NULL, it is connected to NUL: on Windows and
/dev/null on POSIX systems. This is the default for standard input.
If a standard I/O stream is set to SDL_PROCESS_STDIO_APP, it is connected to a new SDL_IOStream that is
available to the application. Standard input will be available as SDL_PROP_PROCESS_STDIN_POINTER and
allows SDL_GetProcessInput(), standard output will be available as SDL_PROP_PROCESS_STDOUT_POINTER and
allows SDL_ReadProcess() and SDL_GetProcessOutput(), and standard error will be available as
SDL_PROP_PROCESS_STDERR_POINTER in the properties for the created process.
If a standard I/O stream is set to SDL_PROCESS_STDIO_REDIRECT, it is connected to an existing
SDL_IOStream provided by the application. Standard input is provided using
SDL_PROP_PROCESS_CREATE_STDIN_POINTER, standard output is provided using
SDL_PROP_PROCESS_CREATE_STDOUT_POINTER, and standard error is provided using
SDL_PROP_PROCESS_CREATE_STDERR_POINTER in the creation properties. These existing streams should be
closed by the application once the new process is created.
In order to use an SDL_IOStream with SDL_PROCESS_STDIO_REDIRECT, it must have
SDL_PROP_IOSTREAM_WINDOWS_HANDLE_POINTER or SDL_PROP_IOSTREAM_FILE_DESCRIPTOR_NUMBER set. This is true
for streams representing files and process I/O.