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BennettSteele

C++ turning "APP.QUIT()" (a string) into actual code

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BennettSteele    493
So i finnished writing some basic network code, and thought about the in game commands. I wanted to be able to turn, lets say

"app.quit()"

and in game make the game quit. I started now by writing

if(ClassDepth[0]=="app")
{
if(ClassDepth[1]=="quit"){app.quit();}
}

but it will take a long time to re write everything. is there any way to make this easier?

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SimonForsman    7642
You could also look at using a map using the command string as the key and a function pointer as the value, it should be enough if you don't have all that many commands to deal with and you don't need to pass parameters to them (If you need to pass parameters to functions them it gets messy really fast), for a large number of commands or more complex commands then something like lua is definitly the way to go. (its extremely easy to execute lua scripts in C or C++ and also quite easy to expose C functions to lua, exposing full C++ classes to lua is a bit more work but there are third party libraries(luabind, tolua for example) that help with that.

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the_edd    2109
Assuming C++:

[code]
struct action : uncopyable
{
action() { }
virtual ~action() { }
virtual void invoke() = 0;
};

struct quit_action : action
{
quit_action(Application &app) : app(app) { }
virtual void invoke() { app.quit(); }

Application &app;
};

// ...

std::map<std::string, shared_ptr<action> > actions;
actions["quit"].reset(new quit_action(the_app));

// ...

bool do_action(const std::string &name)
{
std::map<std::string, shared_ptr<action> >::iterator f = actions.find(name);
if (f != actions.end())
{
(*f)->invoke();
return true;
}
return false;
}
[/code]

If your actions need parameters, you might pass those via a stack, once parsed out of the command string, and each action's invoke() method would attempt to pop them as needed before use (with appropriate checking for underflow).

I'd also agree that Lua is a good idea in principle, but it might actually be more work to do it that way, especially to someone that's relatively new to C++. On the other hand, using a proper scripting language opens up your code to all kinds of other possibilities...

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Cornstalks    7030
Well, this'll be complete overkill for your game, but if you really wanted a nice, extendable solution, [url="http://thrift.apache.org/"]Thrift[/url] is a good option, as it helps manage serializing data (i.e. you give it a data structure and it constructs a compact message representing that data which you can pass through the network) and RPC (Remote Procedure Call, which is exactly what you're asking about now).

[edit]

Google's protocol buffers (protobuf) apparently does RPC too.

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Cornstalks    7030
[quote name='IceBreaker23' timestamp='1329586157' post='4914245']
You could use reflection. It turns strings into real code in runtime. Don´t know how to do this in c++. Java has its own class for this.
[/quote]
You can't. C++ doesn't support reflection.

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Florian22222    618
[quote name='Cornstalks' timestamp='1329598922' post='4914301']
[quote name='IceBreaker23' timestamp='1329586157' post='4914245']
You could use reflection. It turns strings into real code in runtime. Don´t know how to do this in c++. Java has its own class for this.
[/quote]
You can't. C++ doesn't support reflection.
[/quote]

Didnt knew that [img]http://public.gamedev.net//public/style_emoticons/default/biggrin.png[/img] Is there no way to do this?
Oh, i forgot java/c# gets interpreted and c++ is an executeable.

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Antheus    2409
[quote name='IceBreaker23' timestamp='1329749816' post='4914819']
Oh, i forgot java/c# gets interpreted and c++ is an executeable.
[/quote]
The distinction isn't all that useful, both Java and C# VMs run mostly native code, same as C++ binary. They just defer the compilation until code runs. And even then it's possible to force most compilation upfront.

On Android, Java is statically compiled, exactly the same way as C++.

On most modern x86 CPUs even native code is "interpreted", at very least the instructions that CPU executes are defined via microcode rather than being implemented directly.

[quote]Didnt knew that [img]http://public.gamedev.net//public/style_emoticons/default/biggrin.png[/img] Is there no way to do this?[/quote]

Of course there is, it's just a bit of work. Structure data must either be manually defined or somehow generated by compiler or some other tool.

C++ doesn't offer reflection out-of-box due to optimization. A compiler is free to remove anything it deems redundant, including structures and functions. Full reflection would require preserving even unused parts. Templates in particular cause unacceptable overhead without such optimization.

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Florian22222    618
[quote name='Antheus' timestamp='1329751108' post='4914826']
[quote name='IceBreaker23' timestamp='1329749816' post='4914819']
Oh, i forgot java/c# gets interpreted and c++ is an executeable.
[/quote]
The distinction isn't all that useful, both Java and C# VMs run mostly native code, same as C++ binary. They just defer the compilation until code runs. And even then it's possible to force most compilation upfront.

On Android, Java is statically compiled, exactly the same way as C++.

On most modern x86 CPUs even native code is "interpreted", at very least the instructions that CPU executes are defined via microcode rather than being implemented directly.

[quote]Didnt knew that [img]http://public.gamedev.net//public/style_emoticons/default/biggrin.png[/img] Is there no way to do this?[/quote]

Of course there is, it's just a bit of work. Structure data must either be manually defined or somehow generated by compiler or some other tool.

C++ doesn't offer reflection out-of-box due to optimization. A compiler is free to remove anything it deems redundant, including structures and functions. Full reflection would require preserving even unused parts. Templates in particular cause unacceptable overhead without such optimization.
[/quote]

Really usefull knowledge :D
Thank you.

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bubu LV    1436
[quote name='Antheus' timestamp='1329751108' post='4914826']On Android, Java is statically compiled, exactly the same way as C++.[/quote]
What do you mean "exactly the same way as C++" ? On Android Java is compiled exactly same as for desktop - to bytecode. During runtime bytecodes gets interpreted and hotspots are JITed to native machine code. So that is not exactly same as C++, which gets compiled completely to machine code on development host.

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Antheus    2409
[quote name='Martins Mozeiko' timestamp='1329856250' post='4915254']
[quote name='Antheus' timestamp='1329751108' post='4914826']On Android, Java is statically compiled, exactly the same way as C++.[/quote]
What do you mean "exactly the same way as C++" ? On Android Java is compiled exactly same as for desktop - to bytecode. During runtime bytecodes gets interpreted and hotspots are JITed to native machine code. So that is not exactly same as C++, which gets compiled completely to machine code on development host.
[/quote]
My bad, I was thinking of something else.

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