So, I have two classes...Very basic in structure. I try to import one into the other, and declare a new object of that class type...however, it seems to read the class name as the name of a variable?!
The header class provided below will not read the "ApplicationManager" class properly.
Code:
####ifndef _GAME_H_
####define _GAME_H_
####include "application.h"
####include "applicationmanager.h"
class Game : public Application
{
public:
Game();
~Game();
void LoadContent() override;
void UnloadContent() override;
void Draw() override;
private:
//int ApplicationManager; //WHY DOES THIS COMPILE??!
ApplicationManager management; //This DOES NOT WORK?
};
####endif
Here is the header for the "ApplicationManager" class.
Code:
####ifndef _APPMANAGER_H_
####define _APPMANAGER_H_
####include "game.h"
####include "application.h"
class ApplicationManager
{
public:
ApplicationManager(void);
~ApplicationManager(void);
private:
};
####endif
The error that occurs, tells me that I need a ";" before "management", and that "ApplicationManager" is missing a type specifier, so it is assumed to be default-type int.
...any ideas why it won't compile properly? Can someone else try this and report the results? I copied the code, and pasted it in a different solution, to see if something became corrupted....it still didn't work.
You have a cyclic reference. When game.h is included from applicationmanager.h, the ApplicationManager class has not yet been read by the compiler.
To fix, remove the line
#include "game.h"
from applicationmanager.h.
Why do you have circular dependency between Game.h and AppicationManager.h?
Aside from that, I'd say check your header guard (#ifdef _*_H) in Application.h. A fairly often occurence in C++, when copy/pasting code or copying files, is to forget to change the header guard define name for a new class, so you end up with two different headers guarded by the same define. In which case, if both are included into some other file, only the first will actually be expanded into anything useful.
THe error message is some what misleading. It basically says "For some reason (probably an error in the referenced type) I cannot recognize the type you're using (in you case ApplicationManager)".
If you need ApplicationManager to know about Game make a pure virtual base class (interface in other terms) and have Game inherit from that (with out extending the interface) and have ApplicationManager include the base class header file
Related
I'm programming in Visual C++ 2010. I've got a example.h example.cpp and Form1.h.
Basically, I've pasted bits of code. I'm not able to include Form1.h in the example.h file, not sure why. But The main question is how do I call Test (which is in form1.h) from example.cpp? What would be the syntax? Is it possible to do this?
My Form1.h
#include "example.h"
public ref class Form1 : public System::Windows::Forms::Form
{
public: void Test(void)
{
// Does something
}
}
My example.cpp
#include "example.h"
#include "Form1.h"
Test(); // would like to call Test from here.
You have two problems here:
You must call functions from inside of another function. The code you currently have in your example.cpp file is invalid, because you are trying to call the Test() function at global scope.
Make it look like this instead:
int main()
{
Test();
return 0;
}
This also solves the problem that you don't have a main function, which is the entry point to any C++ application.
More generally, I would strongly recommend using one of the project templates that comes with Visual Studio to get started (rather than copying and pasting random bits of code, like you said). That ensures that you have all of the things you need to get started, like an entry point. Once you have a solid foundation, you can start building up from there.
You might also find it useful to obtain either a book on C++/CLI or an online tutorial (such as this one: Hello C++/CLI, Part 1 and Hello C++/CLI, Part 2).
Your Test function is a member function of the Form1 class, which means that you need an object of that class in order to call it. Thus, the code should actually look like this:
int main()
{
Form1^ frm = gcnew Form1();
frm.Test();
return 0;
}
Alternatively, you could work around this by making the Test() function a static function. This would allow you to call it without having an instance of the class:
public ref class Form1 : public System::Windows::Forms::Form
{
public: static void Test(void)
{
// Does something
}
}
// ...
int main()
{
Form1::Test();
return 0;
}
However, beware that this means you cannot access any other members of the Form1 class inside of the Test() function (because there is no this pointer).
This should all be explained in whatever book/tutorial you decide to use to learn C++/CLI—search for a chapter about "Classes" or "Object-Oriented Design".
I use C++/CLI to link between a .NET application and a dynamically loaded C dll.
So far all access to the DLL is instance based.
The class
namespace NxCore {
public class NativeConnector {
has variable for various references to methods:
HMODULE hLib;
NxCoreProcessTape pfNxProcessTape;
NxCorePriceToDouble pfNxPriceToDouble;
NxCoreGetDefinedString pfNxCoreGetDefinedString;
NxCoreGetSymbolAtom32 pfNxGetSymbolAtom32;
NxCoreStateGetMMQuotes pfNxStateGetMmQuotes;
I load those in a connect method:
hLib = ::LoadLibrary("NxCoreAPI.dll");
then
pfNxProcessTape = (NxCoreProcessTape)::GetProcAddress(hLib, cszNxCoreProcessTape);
pfNxPriceToDouble = (NxCorePriceToDouble)::GetProcAddress(hLib, cszNxCorePriceToDouble);
pfNxCoreGetDefinedString = (NxCoreGetDefinedString)::GetProcAddress(hLib, cszNxCoreGetDefinedString);
etc.
Now I need to move that to multi instances, so I want to load on first connect, unload on last disconnect. This means the variables must go static.
In C# I would just make them static. I try one:
static HMODULE hLib;
and linking fails:
4>NativeConnector.obj : error LNK2020: unresolved token (0A00006D) "private: static struct HINSTANCE__ * NxCore::NativeConnector::hLib" (?hLib#NativeConnector#NxCore#Connectivity#Tradex##0PAUHINSTANCE__##A)
Anyone an idea how to fix it? The header file is used on the .cpp file, so - it should not have different definitions.
Anyone can tell he how to fix that issue? As i said - I want to move the variables to be static and then use "usage counting" myself to make sure that I release on last disconnect.
From the code shown I'm not exactly clear on whether the problem occurs in a ref class (.NET class) or a native C++ class.
Here is my advice assuming a native type: You need to define the declared member
header
struct X
{
static int s_data;
};
cpp source:
#include "X.h"
int X::s_data /* = 42 */;
For ref types I'd actually expect the same semantics for static as with C#
Is it possible to extend or modify the code of a C# class at runtime?
My question specifically revolves around Monkey Patching / Duck Punching or Meta Object Programming (MOP), as it happens in scripting languages such as Groovy, Ruby etc.
For those still stumbling on this question in the present day, there is indeed a present-day library called Harmony that relatively-straightforwardly enables such monkey-patching at runtime. Its focus is on video game modding (particularly games built with Unity), but there ain't much stopping folks from using it outside of that use case.
Copying the example from their introduction, if you have an existing class like so:
public class SomeGameClass
{
public bool isRunning;
public int counter;
private int DoSomething()
{
if (isRunning)
{
counter++;
}
return counter * 10;
}
}
Then Harmony can patch it like so:
using HarmonyLib;
using Intro_SomeGame;
public class MyPatcher
{
// make sure DoPatching() is called at start either by
// the mod loader or by your injector
public static void DoPatching()
{
var harmony = new Harmony("com.example.patch");
harmony.PatchAll();
}
}
[HarmonyPatch(typeof(SomeGameClass))]
[HarmonyPatch("DoSomething")]
class Patch01
{
static AccessTools.FieldRef<SomeGameClass, bool> isRunningRef =
AccessTools.FieldRefAccess<SomeGameClass, bool>("isRunning");
static bool Prefix(SomeGameClass __instance, ref int ___counter)
{
isRunningRef(__instance) = true;
if (___counter > 100)
return false;
___counter = 0;
return true;
}
static void Postfix(ref int __result)
{
__result *= 2;
}
}
Here, we have a "prefix" patch which gets inserted before the original method runs, allowing us to set variables within the method, set fields on the method's class, or even skip the original method entirely. We also have a "postfix" patch which gets inserted after the original method runs, and can manipulate things like the return value.
Obviously this ain't quite as nice as the sorts of monkey-patching you can do in e.g. Ruby, and there are a lot of caveats that might hinder its usefulness depending on your use case, but in those situations where you really do need to alter methods, Harmony's a pretty proven approach to doing so.
Is it possible to extend or modify the code of a C# class at run-time?
No it is not possible to do this in .NET. You could write derived classes and override methods (if they are virtual) but you cannot modify an existing class. Just imagine if what you were asking was possible: you could modify the behavior of some existing system classes like System.String.
You may also take a look at Extension methods to add functionality to an existing class.
You can add functionality, but you cannot change or remove functionality.
You can extend classes by adding extra methods, but you cannot override them because added methods have always lower priority than existing ones.
For more info, check Extension Methods in C# Programming Guide.
Using ildasm and a C# program e.g.
static void Main(string[] args)
{
}
gives:
.method private hidebysig static void Main(string[] args) cil managed
{
.entrypoint
// Code size 2 (0x2)
.maxstack 8
IL_0000: nop
IL_0001: ret
} // end of method Program::Main
What does the hidebysig construct do?
From ECMA 335, section 8.10.4 of partition 1:
The CTS provides independent control
over both the names that are visible
from a base type (hiding) and the
sharing of layout slots in the derived
class (overriding). Hiding is
controlled by marking a member in the
derived class as either hide by name
or hide by name-and-signature. Hiding
is always performed based on the kind
of member, that is, derived field
names can hide base field names, but
not method names, property names, or
event names. If a derived member is
marked hide by name, then members of
the same kind in the base class with
the same name are not visible in the
derived class; if the member is marked
hide by name-and-signature then only a
member of the same kind with exactly
the same name and type (for fields) or
method signature (for methods) is
hidden from the derived class.
Implementation of the distinction
between these two forms of hiding is
provided entirely by source language
compilers and the reflection library;
it has no direct impact on the VES
itself.
(It's not immediately clear from that, but hidebysig means "hide by name-and-signature".)
Also in section 15.4.2.2 of partition 2:
hidebysig is supplied for the use of
tools and is ignored by the VES. It
specifies that the declared method
hides all methods of the base class
types that have a matching method
signature; when omitted, the method
should hide all methods of the same
name, regardless of the signature.
As an example, suppose you have:
public class Base
{
public void Bar()
{
}
}
public class Derived : Base
{
public void Bar(string x)
{
}
}
...
Derived d = new Derived();
d.Bar();
That's valid, because Bar(string) doesn't hide Bar(), because the C# compiler uses hidebysig. If it used "hide by name" semantics, you wouldn't be able to call Bar() at all on a reference of type Derived, although you could still cast it to Base and call it that way.
EDIT: I've just tried this by compiling the above code to a DLL, ildasming it, removing hidebysig for Bar() and Bar(string), ilasming it again, then trying to call Bar() from other code:
Derived d = new Derived();
d.Bar();
Test.cs(6,9): error CS1501: No overload for method 'Bar' takes '0' arguments
However:
Base d = new Derived();
d.Bar();
(No compilation problems.)
As per THE SKEET's answer, in addition the reason for this is that Java and C# allow the client of a class to call any methods with the same name, including those from base classes. Whereas C++ does not: if the derived class defines even a single method with the same name as a method in the base class, then the client cannot directly call the base class method, even if it doesn't take the same arguments. So the feature was included in CIL to support both approaches to overloading.
In C++ you can effectively import one named set of overloads from the base class with a using directive, so that they become part of the "overload set" for that method name.
According to Microsoft Docs
When a member in a derived class is declared with the C# new modifier
or the Visual Basic Shadows modifier, it can hide a member of the same
name in the base class. C# hides base class members by signature. That
is, if the base class member has multiple overloads, the only one that
is hidden is the one that has the identical signature. By contrast,
Visual Basic hides all the base class overloads. Thus, IsHideBySig
returns false on a member declared with the Visual Basic Shadows
modifier, and true on a member declared with the C# new modifier.
I have a C++/CLI class library project in VS2005 that i am having some problems with. I have defined a class called Languages which is a an enum class. which looks like this:
"Language.cpp"
namespace Company
{
namespace product
{
public eunm class Languages : int
{
English = 1,
German = 2,
//etc for other languages
};
}
};
I then have another class that tries to references this which lives in the same namespace:
"Language.cpp"
namespace Company
{
namespace product
{
public class LanguageConsumer
{
public:
LanguageConsumer()
{
}
public:
Languages DoSomething(Languages input)
{
if (input == Languages::English)
{
//Do something and return
}
};
}
};
However my project doensn't compile. From what i can figure out the different classes can't see each other even thought they are in the same namespace. I assume that i might need to have header files and #includes for the header files but i just don't know enough about C++/CLI to be sure (i come from C# background with hardly any C experience) and i have tried as many different combinations as i can think of. I'm sure i'm missing something very obvious to anybody who knows what they are doing, but alas i do not.
Thanks in advance.
C++/CLI still compiles like C++, file files are compiled separately and then linked together. This is different from C# which compiles all the files together. At compile time the files don't know about each other so the code doesn't compile (what is this enum?!). You need to have the enum definition in the same file (compilation unit) as the class.
The simple way to do this is to move the code into the same file. The header file solution is to move the enum definition into a header file and then include it (#include) in the other file. #include inserts the text of another file, giving the same effect.