I need help with C# programming; I am new to it and I come from C background. I have a Console Application like this:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace Add_Function
{
class Program
{
static void Main(string[] args)
{
int a;
int b;
int c;
Console.WriteLine("Enter value of 'a':");
a = Convert.ToInt32(Console.ReadLine());
Console.WriteLine("Enter value of 'b':");
b = Convert.ToInt32(Console.ReadLine());
//why can't I not use it this way?
c = Add(a, b);
Console.WriteLine("a + b = {0}", c);
}//END Main
public int Add(int x, int y)
{
int result = x + y;
return result;
}//END Add
}//END Program
}//END Add_Function
It gives me this error on the line that I call Add():
An object reference is required for the non-static field, method, or property 'Add_Function.Program.Add(int, int)'
Can anyone please explain to me why I have this problem. Is this because the architecture of C# is different than C, and the way I call it is wrong? Thanks.
Note: in C# the term "function" is often replaced by the term "method". For the sake of this question there is no difference, so I'll just use the term "function".
The other answers have already given you a quick way to fix your problem (just make Add a static function), but I'd like to explain why.
C# has a fundamentally different design paradigm than C. That paradigm is called object-oriented programming (OOP). Explaining all the differences between OOP and functional programming is beyond the scope of this question, but here's the short version as it applies to you.
Writing your program in C, you would have created a function that adds two numbers, and that function would exist independently and be callable from anywhere. In C# most functions don't exist independently; instead, they exist in the context of an object. In your example code, only an instance (an object) of the class Program knows how to perform Add. Said another way, you have to create an instance of Program, and then ask Program to perform an Add for you.
The solutions that people gave you, using the static keyword, route around that design. Using the static keyword is kind of like saying, "Hey, this function I'm defining doesn't need any context/state, it can just be called." Since your Add function is very simple, this makes sense. As you start diving deeper into OOP, you're going to find that your functions get more complicated and rely on knowing their state/context.
My advice: Pick up an OOP book and get ready to switch your brain from functional programming to OOP programming. You're in for a ride.
You should either make your Add function static like so:
static public int Add(int x, int y)
{
int result = x + y;
return result;
} //END Add
static means that the function is not class instance dependent. So you can call it without needing to create a class instance of Program class.
or you should create in instance of your Program class, and then call Add on this instance. Like so:
Program prog = new Program();
prog.Add(5,10);
This code gives you an error because your Add function needs to be static:
static public int Add(int x, int y)
In C# there is a distinction between functions that operate on instances (non-static) and functions that do not operate on instances (static). Instance functions can call other instance functions and static functions because they have an implicit reference to the instance. In contrast, static functions can call only static functions, or else they must explicitly provide an instance on which to call a non-static function.
Since public static void Main(string[] args) is static, all functions that it calls need to be static as well.
Because your function is an instance or non-static function you should create an object first.
Program p=new Program();
p.Add(1,1)
What that build error is telling you, that you have to either have an instance of Program or make Add static.
Note: in C# the term "function" is often replaced by the term "method". For the sake of this question there is no difference, so I'll just use the term "function".
Thats not true. you may read about (func type+ Lambda expressions),( anonymous function"using delegates type"),(action type +Lambda expressions ),(Predicate type+Lambda expressions). etc...etc...
this will work.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
int a;
int b;
int c;
Console.WriteLine("Enter value of 'a':");
a = Convert.ToInt32(Console.ReadLine());
Console.WriteLine("Enter value of 'b':");
b = Convert.ToInt32(Console.ReadLine());
Func<int, int, int> funcAdd = (x, y) => x + y;
c=funcAdd.Invoke(a, b);
Console.WriteLine(Convert.ToString(c));
}
}
}
Just make your Add function static by adding the static keyword like this:
public static int Add(int x, int y)
you have to make you're function static like this
namespace Add_Function
{
class Program
{
public static void(string[] args)
{
int a;
int b;
int c;
Console.WriteLine("Enter value of 'a':");
a = Convert.ToInt32(Console.ReadLine());
Console.WriteLine("Enter value of 'b':");
b = Convert.ToInt32(Console.ReadLine());
//why can't I not use it this way?
c = Add(a, b);
Console.WriteLine("a + b = {0}", c);
}
public static int Add(int x, int y)
{
int result = x + y;
return result;
}
}
}
you can do Program.Add instead of Add
you also can make a new instance of Program by going like this
Program programinstance = new Program();
The reason why you have the error is because your add function is defined after your using it in main if you were to create a function prototype before main up above it with public int Add(int x, int y); or you could just copy and paste your entire Add function above main cause main is where the compiler starts execution so doesn't it make sense to declare and define a function before you use it hope that helps. :D
static void Main(string[] args)
{
Console.WriteLine("geef een leeftijd");
int a = Convert.ToInt32(Console.ReadLine());
Console.WriteLine("geef een leeftijd");
int b = Convert.ToInt32(Console.ReadLine());
int einde = Sum(a, b);
Console.WriteLine(einde);
}
static int Sum(int x, int y)
{
int result = x + y;
return result;
}
static void Main(string[] args)
{
Console.WriteLine("geef een leeftijd");
int a = Convert.ToInt32(Console.ReadLine());
Console.WriteLine("geef een leeftijd");
int b = Convert.ToInt32(Console.ReadLine());
int einde = Sum(a, b);
Console.WriteLine(einde);
}
static int Sum(int x, int y)
{
int result = x + y;
return result;
I'm trying to pass a function pointer from C# into C++/CLI and getting a windows compiler error stating that the ManagedTakeCallback function is not supported by this language (C#)--I define the ManagedTakeCallback in the C++/CLI interop. My code looks like
C# application:
namespace ManagedConsoleApplication
{
class Callback
{
public delegate double DelegateAdd(double value1, double value2);
public static double CallbackAdd(double value1, double value2)
{
return value1 + value2;
}
public static DelegateAdd delegateCallback = new DelegateAdd(Callback.CallbackAdd); //declare as static to prevent GC
}
class Program
{
// [DllImport("InteropDLL.dll", CallingConvention = CallingConvention.StdCall)]
// public static extern void ManagedCallback(IntPtr pCallback);
static void Main(string[] args)
{
InteropDLL io = new InteropDLL();
Console.WriteLine("The Add return = {0}", io.ManagedAdd(3, 2));
Console.WriteLine("Pass CallBack to Unmanaged code");
Callback cb = new Callback();
IntPtr intptr_delegate = Marshal.GetFunctionPointerForDelegate(Callback.delegateCallback); //convert delegate to function pointer which can be used by unmanaged code
Console.WriteLine("The callback return is {0}", io.ManagedTakeCallback(intptr_delegate));
Console.WriteLine("Please hit Enter to exit");
String value = Console.In.ReadLine();
//Console.WriteLine("End of program ", value);
}
}
}
and,
C++/CLI interop dll h and cpp file:
//HEADER
namespace Interop
{
typedef double (__stdcall *PCallback)(double value1, double value2);
public ref class InteropDLL
{
public:
double ManagedAdd(double value1, double value2);
public:
double ManagedTakeCallback(PCallback pCallback);
};
}
//CPP
double Interop::InteropDLL::ManagedAdd(double value1, double value2)
{
return NativeAdd(value1, value2);
}
double Interop::InteropDLL::ManagedTakeCallback(PCallback pCallback)
{
return NativeTakeCallback();
}
The C++/CLI interop layer then calls a C DLL. I'm able to call ManagedAdd interop function; however, if ManagedTakeCallback is added, there is a windows compiler error. I suspect that the C# application is not marshaling in the function pointer correctly via ManagedTakeCallback function or that the signature is not correct on the C++/CLI side? I would greatly appreciate any insight.
Here is comment from on site:
"But C# doesn’t suport C++ function pointer, so we cannot invoke a C++ function pointer here. C# only has Delegate objects and we have to convert the function pointer to Delegate by Marshal.GetDelegateForFunctionPointer. It is declared in System.Runtime.InteropServices as follows:
public static Delegate GetDelegateForFunctionPointer (
IntPtr ptr,
Type t)
for full answer look at link:
http://www.codeproject.com/Articles/27298/Dynamic-Invoke-C-DLL-function-in-C
I suppose I have to create a managed C++ code to wrap the native C++. But I have the problem while trying to wrap an array used in function parameter whose type is defined in native C++. The native C++ code is as follows:
//unmanageCPP.h
class __declspec(dllexport) unmanageMoney
{
public:
unmanageMoney(int a, int b) { rmb = a; dollar = b; }
unmanageMoney() { rmb = 0; dollar = 0; }
int rmb;
int dollar;
};
class __declspec(dllexport) unmanageSum
{
public:
//how to wrap this funciton?
int addDollar(unmanageMoney a[], unmanageMoney b[]);
};
//unmanageCPP.cpp
#include "unmanaged.h"
int unmanageSum::adddollar(unmanageMoney a[], unmanageMoney b[])
{
return a[0].dollar + b[0].dollar;
}
Could anyone tell me how to write the manageCPP.h? Thanks very much!
Update
I compose the manageCPP.h as follows, but I don't know how to write addDollar()
//first, I wrap the class unmanageMoney for use in manageSum::addDollar()
public ref class manageMoney
{
private:
unmanageMoney* mMoney;
public:
unmanageMoney getMoney()
{
return *mMoney;
}
manageMoney(int a, int b) { mMoney = new unmanageMoney(a, b); }
~manageMoney() { delete mMoney; }
};
public ref class manageSum
{
// TODO: Add your methods for this class here.
private:
unmanageSum *mSum;
public:
manageSum()
{
mSum = new unmanageSum();
}
~manageSum()
{
delete mSum;
}
//it must be wrong if I code like this, for unmanageSun::adddollar() only
// receives unmanageMoney as arguments. So what should I do?
int adddollar(manageMoney a[], manageMoney b[])
{
return mSum->adddollar(a, b);
}
};
You create a C++/CLI source file with
public ref class SomethingOrOther
{
//...
};
and set the compile options to use the /clr option.
Beyond that, it's almost the same as writing native C++. You'll #include the header file for the class you want to reuse, create instances and call their member functions, just the same as normal C++. But anything inside that ref class will be visible to C#.
And you do NOT put __declspec(dllexport) on the class. Not ever. It's useful for functions, but creates misery when used with classes.
I want to use PInvoke to bring to managed side something this:
(C code)
typedef struct{
//some fields...
} A;
type struct{
A* a;
} B;
int getB(B* destination){ //destionation will be an output parameter to C#
//puts an B in 'destination'
return 0;
}
Now, I need a way to tell managed side how to marshalling B from C to C# structure or class. I've tryed many things such as IntPtr fields, MarchalAs atributes, but with no success. I will not expose here the code that I've tryed to keep the question simple. However i could do it as long answers arrive.
If it were me, I would just use unsafe code and use pointers on the C# side:
public unsafe class UnmanagedStuff {
public struct A {
// some fields
}
public struct B {
public A* a;
}
// Add appropriate PInvoke attribute here
public static extern int getB(B* destination);
public static void UseBForSomething() {
B b;
getB(&b);
// Do something with b
}
}
You can do that using the Marshal class.
// Define a C# struct to match the unmanaged one
struct B
{
IntPtr a;
}
[DllImport("dllName")]
extern int getB(IntPtr destination);
B GetB()
{
IntPtr ptrToB = IntPtr.Zero;
getB(ptrToB);
return (B)Marshal.PtrToStructure(ptrToB, typeof(B));
}
I have a C# program that is calling into a native C++ dll.
The C# has a the following struct:
[StructLayout(LayoutKind.Sequential)]
public struct Phenomenon
{
[MarshalAs(UnmanagedType.U1)] public char Type;
[MarshalAs(UnmanagedType.R8)] public double Jd;
[MarshalAs(UnmanagedType.R8)] public double Loc_jd;
[MarshalAs(UnmanagedType.R8)] public double Angle;
[MarshalAs(UnmanagedType.U1)] public char Tran_dir;
[MarshalAs(UnmanagedType.I2)] public Int16 Warning;
}
The C++ program has the following struct definition:
typedef struct
{
char type;
double jd;
double loc_jd;
double angle;
char tran_dir;
short int warning;
} phenomenon;
The C# program instantiates the Phenomenom objects has the following call to the C++ method:
Phenomenon[] phenomena = new Phenomenon[6];
short status = rsttwi_temp(phenomena);
The C++ simply updates the struct and returns. Here is the C++ function:
__declspec(dllexport) short int rsttwi_temp (phenomenon phen[1])
{
phen[0].type = 'Z';
phen[0].jd = 1.1;
phen[0].loc_jd = 2.2;
phen[0].angle = 3.3;
phen[0].tran_dir = 4.4;
phen[0].warning = '0';
return 0;
}
From the C# program when I print out the values of the struct after the call to the C++ function, the struct has not been updated (i.e. it is the same as before the C++ function was called). It seems that the C++ program is able to see the values and update them, but upon return the C# never sees the updates to the values in the struct. Thinking it was a value vs. reference problem, I even tried to do this with a class in the C# program, instead of the struct. Still no luck.
Question:
What marshaling do I need to allow the called C++ function to be able to update the actual struct that was passed to it?
Thank you.
-Greg Edwards
Total Immersion Software
It's not easy to understand why this doesn't work without seeing the definition of your C# function. I'm guessing it looks something like this though
[DllImport("somedll.dll")]
public static extern Int16 rsttwi_temp(Phenomenon[] array);
I don't have much experience working pinvoking a fixed size native array. But what you could do is change the C++ signature to take a pointer instead of a fixed size array and switch the managed code to pass by reference. For example
[DllImport("somedll.dll")]
public static extern Int16 rsttwi_temp(ref Phenomenon value);
__declspec(dllexport) short int rsttwi_temp (phenomenon* phen)
Using in this way works:
C++
__declspec(dllexport) short int rsttwi_temp (phenomenon* phen)
{
phen->jd = 1.1;
phen->loc_jd = 2.2;
phen->angle = 3.3;
phen->warning = 0;
return 0;
}
typedef struct
{
double jd;
double loc_jd;
double angle;
short int warning;
} phenomenon;
C#
[DllImport("somedll.dll", CallingConvention = CallingConvention.Cdecl)]
public static extern Int16 rsttwi_temp(ref Phenomenon value);
[StructLayout(LayoutKind.Sequential)]
public struct Phenomenon
{
[MarshalAs(UnmanagedType.R8)]
public double Jd;
[MarshalAs(UnmanagedType.R8)]
public double Loc_jd;
[MarshalAs(UnmanagedType.R8)]
public double Angle;
[MarshalAs(UnmanagedType.I2)]
public Int16 Warning;
}
C# Call
Phenomenon phenomena = new Phenomenon();
short status = rsttwi_temp(ref phenomena);
C# char != C++ char.
C# char == C++ wchar_t
C++ char == C# byte