I am wrapping some C++ code in managed C++ to access it in C#: I can not figure out how to make operators properly work in C#
I create in managed C++:
public ref class ClassCLI
{
public:
double val;
ClassCLI() {};
void operator ++() { val++; };
double% operator[](int i) { return val; }
};
This works in managed C++:
ClassCLI^ obj = gcnew ClassCLI();
obj++;
obj[0] = 12.0;
But in C#, I can not use the operators ++ or [] directly, I have to use some ugly name that defeats the purpose of operators.
var obj = new ClassCLI();
obj.op_Increment();
obj.op_Subscript(0) = 12.0;
Can one tell me what I am doing wrong ? I says on some posts that operators should be static for C#, it is easy for operator++ but not sure how to do for the operator[]
If you refer to
C++/CLI: how to overload an operator to accept reference types?
How to declare the default indexed property in C++/CLI interface
you can get an idea to implement your ClassCLI class.
Sample implementation:
C++
public ref class ClassCLI
{
public:
double val;
ClassCLI() {};
property double default[int]
{
double get(int index) { return val; }
void set(int index, double value) { val = value; }
}
static ClassCLI^ operator ++(ClassCLI^ c)
{
c->val++;
return c;
};
};
C#:
static void Main()
{
ClassCLI c = new ClassCLI();
Console.WriteLine(c.val);
c++;
Console.WriteLine(c.val);
c[0] = 12;
Console.WriteLine(c.val);
Console.Read();
}
Output:
0
1
12
Related
Recently, I met a problem that how to change "int" value when using the extension method, don't allow use keyword "ref" or "out":
static void Main(string[] args)
{
var a = 5;
var b = 6;
a.Swap(b);
Console.WriteLine("a={0},b={1}", a, b);
Console.ReadKey();
}
I want to implement the Swap method(exchange variable a and variable b) and final output like this:
a = 6，b = 5
Swap method needs to exchange variable a and variable b, The issue is assigned by my teacher.
My answer is :
unsafe static void Swap(this int a, int b)
{
int* pb = &b;
pb += 7;
int* pa = &a;
pa += 8;
int temp = *pa;
*pa = *pb;
*pb = temp;
}
But my teacher said it not good enough. Because the 7 and 8 will be affected by the C# compiler.
I really didn't know how to implements Swap method. I think the integer will be passed by value when passing into Swap, and can't change it unless finding out its original address.
Did I misunderstand something? Your thought would be appreciated.
added:
There is a lot of people said it doesn't make sense, and a lot of questions, I know it doesn't make sense. but it truly can do this. I will paste the answer to bellow after I got the answer from my teacher.
added 20190225
I get an answer from my teacher, below is the complete answer:
internal static class Program
{
static void Main(string[] args)
{
var (a, b) = (5,6);
a.Swap(b);
Console.WriteLine($"a=({a}),b=({b})");
Console.ReadKey();
}
private static void Swap<T>(ref this T op1, in T op2)
where T : struct
{
var temp = op1;
op1 = op2;
RefUnlocker.Unlock(op2) = temp;
}
}
public class RefUnlocker
{
private delegate ref T InToRef<T>(in T arg) where T : struct;
private static ref T RefWrapper<T>(ref T arg) where T : struct => ref arg;
private static readonly MethodInfo _refWrapper = typeof(RefUnlocker)
.GetMethod(nameof(RefWrapper), BindingFlags.Static | BindingFlags.NonPublic);
public static ref T Unlock<T>(in T arg) where T : struct
{
Delegate dgt = Delegate.CreateDelegate(typeof(InToRef<T>), _refWrapper.MakeGenericMethod(typeof(T)));
InToRef<T> itrf = (InToRef<T>)dgt;
return ref itrf(arg);
}
}
C# 7.2 provides a keyword in. The in modifier on parameters, to specify that an argument is passed by reference but not modified by the called method. Adding the in modifier to an argument is a source compatible change.
However you can use Delegate to modify the in parameter.
Thanks to my teacher deeply for this.
It is not at all clear why you are adding 7 and 8 to some pointers.
What do you hope to accomplish with that?
If the extension method is not essential, then the answer is easy!!
As Michael Randall wrote:
static unsafe void Swap(int* pa, int* pb)
{
int temp = *pb;
*pb = *pa;
*pa = temp;
}
// Call this with: Swap(&a,&b);
The best I could do with an extension is:
using System;
public static class Test
{
static unsafe void Swap(this int a, int* pa, int* pb)
{
*pa = *pb;
*pb = a;
}
public static unsafe void Main()
{
var a = 5;
var b = 6;
a.Swap(&a, &b);
Console.WriteLine("a={0},b={1}", a, b);
}
}
IDEOne Code
Results
Success #stdin #stdout 0.01s 131520KB
a=6,b=5
This is only to back up #abelenky's answer, not to be an answer in itself
Just with pointers, no extension, no ref, no out
public unsafe static void Swap(int* a, int* b)
{
var temp = *a;
*a = *b;
*b = temp;
}
Usage
public unsafe static void Main()
{
var a = 5;
var b = 6;
Swap(&a, &b);
Console.WriteLine("a={0},b={1}", a, b);
Console.ReadKey();
}
or another variation with a franken-extensions
public static unsafe class ext
{
public static int Swap(this int a, int* b)
{
var temp = *b;
*b = a;
return temp;
}
}
Usage
var a = 5;
var b = 6;
a = a.Swap(&b);
Console.WriteLine("a={0},b={1}", a, b);
I have following problem. I want to convert an integer value or float value into an byte array. Normaly I use the BitConverter.GetBytes() method.
int i = 10;
float a = 34.5F;
byte[] arr;
arr = BitConverter.GetBytes(i);
arr = BitConverter.GetBytes(a);
Is there a possibility to do this with implicit/explicit methods??
arr = i;
arr = a;
and also the other way around??
i = arr;
a = arr;
You can do it through an intermediate class. The compiler won't do two implicit casts by itself, so you must do one explicit cast and then the compiler will figure out the second one.
The problem is that with implicit casts, you must either cast to or from the type you declare the cast in, and you cannot inherit from sealed classes like 'int'.
So, it is not elegant at all. Extension methods are probably more elegant.
If you declare the class below, you can then do things like:
byte[] y = (Qwerty)3;
int x = (Qwerty) y;
public class Qwerty
{
private int _x;
public static implicit operator byte[](Qwerty rhs)
{
return BitConverter.GetBytes(rhs._x);
}
public static implicit operator int(Qwerty rhs)
{
return rhs._x;
}
public static implicit operator Qwerty(byte[] rhs)
{
return new Qwerty {_x = BitConverter.ToInt32(rhs, 0)};
}
public static implicit operator Qwerty(int rhs)
{
return new Qwerty {_x = rhs};
}
}
you could create extension methods to clean up the calling code a little bit - so you'd end up with:
int i = 10;
float a = 34.5F;
byte[] arr;
arr = i.ToByteArray();
arr = a.ToByteArray();
The code for the extension methods would be something like:
public static class ExtensionMethods
{
public static byte[] ToByteArray(this int i)
{
return BitConverter.GetBytes(i);
}
public static byte[] ToByteArray(this float a)
{
return BitConverter.GetBytes(a);
}
}
I have the following code in C#:
public string Temp
{
get { return sTemp; }
set {
sTemp = value;
this.ComputeTemp();
}
}
Is it possible to convert this and use the get and set this way? I know that you cannot declare like so and I need the ":" to declare but when I try to do this:
public:
std::string Temp
{
get { return sTemp; }
set {
sTemp = value;
this.ComputeTemp();
}
The error I receive is on the first "{" stating expected a ';'. Any suggestions on how to fix it?
Are you using C++/CLI? If so this is the property syntax
public:
property std::string Temp {
std::string get() { return sTemp; }
void set(std::string value) { sTemp = value; this->ComputeTemp(); }
}
If you are trying to use normal C++ then you are out of luck. There is no equivalent feature for normal C++ code. You will need to resort to getter and setter methods
public:
std::string GetTemp() const { return sTemp; }
void SetTemp(const std::string& value) {
sTemp = value;
this->ComputeTemp();
}
To copy paste one of my answers from a similar question:
WARNING: This is a tongue-in-cheek response and is terrible!!!
Yes, it's sort of possible :)
template<typename T>
class Property
{
private:
T& _value;
public:
Property(T& value) : _value(value)
{
} // eo ctor
Property<T>& operator = (const T& val)
{
_value = val;
return(*this);
}; // eo -
operator const T&() const
{
return(_value);
}; // eo ()
};
Then declare your class, declaring properties for your members:
class Test
{
private:
std::string m_Test;
public:
Test() : text(m_Test)
{
};
Property<std::string> text;
};
And call C# style!
Test a;
a.text = "blah";
std::string content = a.text;
In Visual C++ you can use __declspec(property), like this:
public:
__declspec(property(get=get_Temp, put=set_Temp)) std::string Temp;
const std::string& get_Temp { return sTemp; }
void set_Temp(std::string value) {
sTemp = std::move(value);
this->ComputeTemp();
}
Can I overload operators for class A in class B in C#? For example:
class A
{
}
class B
{
public static A operator+(A x, A y)
{
...
}
}
No; one of the parameters must be the containing type.
From section §10.10.2 of the language specification (version 4.0):
The following rules apply to binary operator declarations, where T denotes the instance type of the class or struct that contains the operator declaration:
• A binary non-shift operator must take two parameters, at least one of which must have type T or T?, and can return any type.
You should think about why. Here's one reason.
class A { }
class B { public static A operator+(A first, A second) { // ... } }
class C { public static A operator+(A first, A second) { // ... } }
A first;
A second;
A result = first + second; // which + ???
Here's another:
class A { public static int operator+(int first, int second) { // ... } }
Assume this allowed for a moment.
int first = 17;
int second = 42;
int result = first + second;
Per the specification for operator overload resolution (§7.3.2), A.+ will have precedence over Int32.+. We've just redefined addition for ints! Nasty.
No, you can't. error CS0563: One of the parameters of a binary operator must be the containing type
"In each case, one parameter must be the same type as the class or struct that declares the operator" quote from
Documentation on overloading operators.
Generally saying NO, but you can do something like following, if it helps :)
class A
{
public static A operator +(A x, A y)
{
A a = new A();
Console.WriteLine("A+"); // say A
return a;
}
}
class B
{
public static A operator +(A x, B y)
{
A a = new A();
Console.WriteLine("return in:A,B in out:A in class B+"); // say B
return a;
}
public static A operator +(B x, B y)
{
A a = new A();
Console.WriteLine("return in:B,B in out:A in class B +");
return a;
}
// and so on....
}
B b = new B();
A a = new A();
A a1 = new A();
B b1 = new B();
a = b + b1; // here you call operator of B, but return A
a = a + a1; // here you call operator of A and return A
To understand your problem, can i ask why you want to do that? :)
I have some VERY inefficient code in which many lines appear 4 times as I go through permutations with "<" and ">" operations and a variety of variables and constants. It would seem that there is a way to write the function once and pass in the operators along with the necessarily changing values and"ref" variables. What technique do I have to learn? "Delegates" have been suggested but I don't see how to use them in this manner. This is in C# 2.0, VS2005, but if the technique is generic and can be used with C++ too, that would be great.
Request for some code: The following appears in many guises, with different "<" and ">" signs as well as a mix of "+" and "-" signs:
if (move[check].Ypos - move[check].height / 200.0D < LayoutManager.VISIO_HEIGHT - lcac_c.top)
{
move[check].Ypos = move[check].Ypos + adjust;
.
.
.
In C++, use the std::less and std::greater functors. Both of these methods inherit std::binary_function, so your generic function should accept instances of this type.
In .NET, the equivalent to std::binary_function is Func<T, U, R>. There are no equivalents to std::less and std::greater, but it is fairly trivial to create them. See the following example.
static class Functor
{
static Func<T, T, bool> Greater<T>()
where T : IComparable<T>
{
return delegate(T lhs, T rhs) { return lhs.CompareTo(rhs) > 0; };
}
static Func<T, T, bool> Less<T>()
where T : IComparable<T>
{
return delegate(T lhs, T rhs) { return lhs.CompareTo(rhs) < 0; };
}
}
Note, the above code uses the Func<> class from .NET 3.5. If this is not acceptable, consider defining you own delegate.
C++ invocation example:
void DoWork(const std::binary_function<int, int, bool>& myOperator,
int arg1, int arg2)
{
if (myOperator(arg1, arg2)) { /* perform rest of work */ }
}
void main()
{
DoWork(std::less<int>(), 100, 200);
DoWork(std::greater<int>(), 100, 200);
}
C# invocation example:
void DoWork(Func<int, int, bool> myOperator, int arg1, int arg2)
{
if (myOperator(arg1, arg2)) { /* perform rest of work */ }
}
void main()
{
DoWork(Functor.Less<int>(), 100, 200);
DoWork(Functor.Greater<int>(), 100, 200);
}
EDIT: I corrected the example of the functor class as applying < or > operators to a generic type doesn't work (in the same manner as it does with C++ templates).
In C# use delegates for passing the "<" and ">" operation to the code that's doing the work.
C# Example:
public delegate bool BooleanOperatorDelegate(int a, int b)
class OperatorsImplementer {
public bool OperatorLess(int a, int b) {
return a < b;
}
}
class AnotherOperatorsImplementer {
public bool OperatorLess(int a, int b) {
return (a + 1) < (b - 1);
}
}
class OperatorUser {
int DoSomethingObscene(int a, int b, BooleanOperatorDelegate operator) {
if (operator(a, b)) {
return 5;
}
else {
return -5;
}
}
}
You should also check that the delegate you get as a paramater is not NULL.
This is the C method for doing so:
bool (*operator_func)(float a, float b)
After defining the Enum Operator in the Comparer class
public static class Comparer
{
public static bool IsTrue<T, U>(T value1, Operator comparisonOperator, U value2)
where T : U
where U : IComparable
{
switch (comparisonOperator)
{
case Operator.GreaterThan:
return value1.CompareTo(value2) > 0;
case Operator.GreaterThanOrEqual:
return value1.CompareTo(value2) >= 0;
case Operator.LessThan:
return value1.CompareTo(value2) < 0;
case Operator.LessThanOrEqual:
return value1.CompareTo(value2) <= 0;
case Operator.Equal:
return value1.CompareTo(value2) == 0;
default:
return false;
}
}
public enum Operator
{
GreaterThan = 1,
GreaterThanOrEqual = 2,
LessThan = 3,
LessThanOrEqual = 4,
Equal = 5
}
}
You can make a call like this:
if (IsTrue(var1, Operator.GreaterThanOrEqual, var2))
Console.WriteLine("var1 is greater than var2");
else
Console
.WriteLine("Unfortunately var1 is not greater than or equal var2. Sorry about that.");