If your needs aren't complex, it might be easier to use
SDL_ShowSimpleMessageBox.
This function should be called on the thread that created the parent
window, or on the main thread if the messagebox has no parent. It will
block execution of that thread until the user clicks a button or closes the
messagebox.
This function may be called at any time, even before SDL_Init(). This makes
it useful for reporting errors like a failure to create a renderer or
OpenGL context.
On X11, SDL rolls its own dialog box with X11 primitives instead of a
formal toolkit like GTK+ or Qt.
Note that if SDL_Init() would fail because there isn't any available video
target, this function is likely to fail for the same reasons. If this is a
concern, check the return value from this function and fall back to writing
to stderr if you can.
Create a modal message box.
If your needs aren't complex, it might be easier to use SDL_ShowSimpleMessageBox.
This function should be called on the thread that created the parent window, or on the main thread if the messagebox has no parent. It will block execution of that thread until the user clicks a button or closes the messagebox.
This function may be called at any time, even before SDL_Init(). This makes it useful for reporting errors like a failure to create a renderer or OpenGL context.
On X11, SDL rolls its own dialog box with X11 primitives instead of a formal toolkit like GTK+ or Qt.
Note that if SDL_Init() would fail because there isn't any available video target, this function is likely to fail for the same reasons. If this is a concern, check the return value from this function and fall back to writing to stderr if you can.