int SDL_ShowMessageBox(const SDL_MessageBoxData* messageboxdata,
                       int*                      buttonid)

#include "SDL.h"

int main(int argc, char *argv[])
{
    const SDL_MessageBoxButtonData buttons[] =
    {
        { /* .flags, .buttonid, .text */        0, 0, "no" },
        { SDL_MESSAGEBOX_BUTTON_RETURNKEY_DEFAULT, 1, "yes" },
        { SDL_MESSAGEBOX_BUTTON_ESCAPEKEY_DEFAULT, 2, "cancel" },
    };
    const SDL_MessageBoxColorScheme colorScheme =
    {
        { /* .colors (.r, .g, .b) */
            /* [SDL_MESSAGEBOX_COLOR_BACKGROUND] */
            { 255,   0,   0 },
            /* [SDL_MESSAGEBOX_COLOR_TEXT] */
            {   0, 255,   0 },
            /* [SDL_MESSAGEBOX_COLOR_BUTTON_BORDER] */
            { 255, 255,   0 },
            /* [SDL_MESSAGEBOX_COLOR_BUTTON_BACKGROUND] */
            {   0,   0, 255 },
            /* [SDL_MESSAGEBOX_COLOR_BUTTON_SELECTED] */
            { 255,   0, 255 }
        }
    };
    const SDL_MessageBoxData messageboxdata =
    {
        SDL_MESSAGEBOX_INFORMATION, /* .flags */
        NULL, /* .window */
        "example message box", /* .title */
        "select a button", /* .message */
        SDL_arraysize(buttons), /* .numbuttons */
        buttons, /* .buttons */
        &colorScheme /* .colorScheme */
    };
    int buttonid;
    if (SDL_ShowMessageBox(&messageboxdata, &buttonid) < 0)
    {
        SDL_Log("error displaying message box");
        return 1;
    }
    if (buttonid == -1)
    {
        SDL_Log("no selection");
    }
    else
    {
        SDL_Log("selection was %s", buttons[buttonid].text);
    }
    return 0;
}