The MessageBox() alternative for Gtk4

README.md

Why

You are writing a game in, say GLFW or SDL. Somehow you want to show a fatal error message to the user, preferrably in native style. How?

• On Windows, you can simply call MessageBox() to show such message.
• On Linux, you can use the method below.
• On other platforms, well it's your homework.

How to compile

Just compile it without any flags should work.

# Use gcc
g++ message-box.cpp
./a.out

# Use clang
clang++ message-box.cpp
./a.out

If there are any linking error, you may need to supply -ldl to the compiler.

message-box.cpp

#include <dlfcn.h>
#include <assert.h>

namespace gtk
{
    struct Object;
    using Unref = auto (Object*) -> void;
    using Try_Init = auto () -> bool;
    using Iterate_Main_Context = auto (Object*, bool) -> bool;
    using New_Alert_Dialog = auto (char const* fmt, ...) -> Object*;
    using Show_Alert_Dialog = auto (Object* self, Object* parent) -> void;
    using Set_Alert_Dialog_Detail = auto (Object*, char const*) -> void;
    using Count_List_Items = auto (Object*) -> unsigned;
    using List_Toplevels = auto () -> Object*;

    auto show_messgage_box(char const* title, char const* message) -> void
    {
        auto lib = dlopen("/usr/lib/libgtk-4.so", RTLD_LAZY | RTLD_LOCAL);
        assert(lib);

        auto unref = (gtk::Unref*) dlsym(lib, "g_object_unref");
        auto iterate_main_context = (gtk::Iterate_Main_Context*) dlsym(lib, "g_main_context_iteration");
        auto try_init = (gtk::Try_Init*) dlsym(lib, "gtk_init_check");
        auto new_alert_dialog = (gtk::New_Alert_Dialog*) dlsym(lib, "gtk_alert_dialog_new");
        auto show_alert_dialog = (gtk::Show_Alert_Dialog*) dlsym(lib, "gtk_alert_dialog_show");
        auto set_alert_dialog_detail = (gtk::Set_Alert_Dialog_Detail*) dlsym(lib, "gtk_alert_dialog_set_detail");
        auto list_toplevels = (gtk::List_Toplevels*) dlsym(lib, "gtk_window_get_toplevels");
        auto count_list_items = (gtk::Count_List_Items*) dlsym(lib, "g_list_model_get_n_items");

        assert(unref);
        assert(iterate_main_context);
        assert(try_init);
        assert(new_alert_dialog);
        assert(show_alert_dialog);
        assert(set_alert_dialog_detail);
        assert(list_toplevels);
        assert(count_list_items);

        if (!try_init()) return;
        
        auto dialog = new_alert_dialog("%s", title);
        set_alert_dialog_detail(dialog, message);
        show_alert_dialog(dialog, nullptr);

        while (count_list_items(list_toplevels()) > 0u) {
            iterate_main_context(nullptr, true);
        }

        unref(dialog);
        dlclose(lib);
    }
}

int main()
{
    gtk::show_messgage_box("Hi", "Hello world!");
    gtk::show_messgage_box("Fatal Error", "Something bad happened.\nThere is nothing you can do.");
}