Programming Forums > Application Development > C#

Arla · Jan 3rd, 2007, 6:56 PM

I'm not sure if I'm being totally thick here, or just this is really something I can't do in C#

I want to create an array that contains a string, an int and a long (say for example) and I just can't work out how I could do this, I know that

string[3][] would create an array of all strings, would I have to do something like

object[3][] and then object[0][] = string[]

something like that?

Tim · Jan 3rd, 2007, 7:22 PM

Do you mean you want an array that contains each of the characters form a string?

Or do you want an array where each element contains a string?

DaWei · Jan 3rd, 2007, 7:39 PM

Arrays, in C#, contain elements of a single type. You can't have an array that holds a string in one element, and integer in another element, and a buffalo in another.

Tim · Jan 3rd, 2007, 7:44 PM

My God I was being thick. It did not occur to me that that was what Arla ment.

Well he could just have an array of objects. It would need some casts and would need to be managed as you need to know exactly what each element really is. Its not really an ideal solution.

If you could tell us the problem you are trying to solve Arla then there might be a better way.

Arla · Jan 3rd, 2007, 7:52 PM

Tim,

Not sure I can easily explain the problem, it was more one of theories and potential ways to do something rather than "oh my word I can't possibly do this" just trying to determine optimal solutions, as such I think I've got it now, just added the required data together to make one "super" type.

Arla · Jan 3rd, 2007, 7:53 PM

Quote:

Originally Posted by DaWei

Arrays, in C#, contain elements of a single type. You can't have an array that holds a string in one element, and integer in another element, and a buffalo in another.

Dawei,

Thanks for confirming, it's what I'd figured/feared and I can do what I want another route, just wanted to check that I wasn't overly complicating something.

Tim · Jan 3rd, 2007, 8:05 PM

If you have an array of object you can put anything you want into the array

The problem comes when you want to get data out, you have to know the type that the data was before it went into the array and was cased to type object.

C# is a statically typed langage so you cant just have a variable that is everything to everyone. It also is dynamically type checked so if you try to make a string do something that only an integer can do it will fail.

(Toggle Plain Text)

	object[] myArray = new object[10];
	myArray[0] = 20;
	myArray[1] = "Hello World";
	myArray[2] = 3.14;
	
           //The cast must be correct here.		
	int i = (int)myArray[0];
	string s = (string)myArray[1];
	double d = (double)myArray[2];

This probably wont solve your problem as i think you want it so you can put anything in and then get it out without knowing what it was to start with.

edit: If you look into reflection you may be able to tell the type for the element at runtime and so have the correct cast.

ChiHappens · Jan 4th, 2007, 3:57 PM

Maybe you are looking for a structure.

(Toggle Plain Text)

public struct MyStruct
{
  public int ID;
  public string Name;
  public double Value;
}
public MyStruct[] MyStructArray = new MyStruct[10]; // using array
or
public System.Collections.ArrayList MyStructArray = new System.Collections.ArrayList();

lectricpharaoh · Jan 4th, 2007, 11:14 PM

I guess this is what I get for not being so active here lately, as both my suggestions have already been made.

@Arla: If you have a fixed relationship between the types, for example, a 'unit' of data is composed of a string, an int, and a long, then structs (or classes) are definitely the way to go. If you won't know the types beforehand, then you can do what Tim suggested, and stuff everything into a collection (array or otherwise) of objects. Then, you can use the GetType() method to determine the type at runtime, and process it as appropriate. To get the type at compile time, use the typeof operator. For example, assume you've stuffed in a bunch of elements into an array. You could probably do something like this:

(Toggle Plain Text)

for(int x=0; x<array.length; ++x)
{
  if(array[x].GetType() == typeof(string))
    Console.WriteLine("Type is string");
  else if(array[x].GetType() == typeof(int))
    Console.WriteLine("Type is int");
  else if(array[x].GetType() == typeof(long))
    Console.WriteLine("Type is long");
}

Obviously, instead of simply outputting a message, you'll want to do appropriate processing, but hopefully, you get the idea. This shows that you can (in a manner) have an array with elements of different types. Strictly speaking, this is not true, as every element is of type object (or whatever the base class in question is; you needn't go quite that far up the object hierarchy in all cases). Remember that an object of a subclass is also an object of the parent class (a Car is also a Vehicle), but the inverse is not necessarily true. Thus, there is the test to see which exact subclass the element is, in order to process it properly.

If you're curious, you can also use the GetMethods(), GetMembers(), and GetProperties() methods of the System.Type class (both GetType() and typeof return a System.Type, so you can call these methods on the returned object). The last one is especially handy (it's an integral part of the mechanism through which certain data-bound controls can determine the various fields- ie, columns- to display). This page gives further details.

Jan 3rd, 2007, 6:56 PM	#1
Arla Professional Programmer Join Date: Mar 2005 Posts: 302 Rep Power: 4	Array question I'm not sure if I'm being totally thick here, or just this is really something I can't do in C# I want to create an array that contains a string, an int and a long (say for example) and I just can't work out how I could do this, I know that string[3][] would create an array of all strings, would I have to do something like object[3][] and then object[0][] = string[] something like that?

Jan 3rd, 2007, 7:39 PM	#3
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	Arrays, in C#, contain elements of a single type. You can't have an array that holds a string in one element, and integer in another element, and a buffalo in another. __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

Jan 3rd, 2007, 8:05 PM	#7
Tim Unverified User Join Date: Dec 2006 Location: Bristol UK Posts: 19 Rep Power: 0	If you have an array of object you can put anything you want into the array The problem comes when you want to get data out, you have to know the type that the data was before it went into the array and was cased to type object. C# is a statically typed langage so you cant just have a variable that is everything to everyone. It also is dynamically type checked so if you try to make a string do something that only an integer can do it will fail. (Toggle Plain Text) object[] myArray = new object[10]; myArray[0] = 20; myArray[1] = "Hello World"; myArray[2] = 3.14; //The cast must be correct here. int i = (int)myArray[0]; string s = (string)myArray[1]; double d = (double)myArray[2]; object[] myArray = new object[10]; myArray[0] = 20; myArray[1] = "Hello World"; myArray[2] = 3.14; //The cast must be correct here. int i = (int)myArray[0]; string s = (string)myArray[1]; double d = (double)myArray[2]; This probably wont solve your problem as i think you want it so you can put anything in and then get it out without knowing what it was to start with. edit: If you look into reflection you may be able to tell the type for the element at runtime and so have the correct cast.

Jan 4th, 2007, 3:57 PM	#8
ChiHappens Programmer Join Date: Sep 2005 Location: Brevard, NC Posts: 35 Rep Power: 0	Maybe you are looking for a structure. (Toggle Plain Text) public struct MyStruct { public int ID; public string Name; public double Value; } public MyStruct[] MyStructArray = new MyStruct[10]; // using array or public System.Collections.ArrayList MyStructArray = new System.Collections.ArrayList(); public struct MyStruct { public int ID; public string Name; public double Value; } public MyStruct[] MyStructArray = new MyStruct[10]; // using array or public System.Collections.ArrayList MyStructArray = new System.Collections.ArrayList(); __________________ http://www.starshipcombatsimulator.com They mostly come at night...mostly.

Jan 4th, 2007, 11:14 PM	#9
lectricpharaoh Caffeinated Neural Net Join Date: Jun 2005 Location: Wet west coast of Canada Posts: 1,126 Rep Power: 5	I guess this is what I get for not being so active here lately, as both my suggestions have already been made. @Arla: If you have a fixed relationship between the types, for example, a 'unit' of data is composed of a string, an int, and a long, then structs (or classes) are definitely the way to go. If you won't know the types beforehand, then you can do what Tim suggested, and stuff everything into a collection (array or otherwise) of objects. Then, you can use the GetType() method to determine the type at runtime, and process it as appropriate. To get the type at compile time, use the typeof operator. For example, assume you've stuffed in a bunch of elements into an array. You could probably do something like this: (Toggle Plain Text) for(int x=0; x<array.length; ++x) { if(array[x].GetType() == typeof(string)) Console.WriteLine("Type is string"); else if(array[x].GetType() == typeof(int)) Console.WriteLine("Type is int"); else if(array[x].GetType() == typeof(long)) Console.WriteLine("Type is long"); } for(int x=0; x<array.length; ++x) { if(array[x].GetType() == typeof(string)) Console.WriteLine("Type is string"); else if(array[x].GetType() == typeof(int)) Console.WriteLine("Type is int"); else if(array[x].GetType() == typeof(long)) Console.WriteLine("Type is long"); } Obviously, instead of simply outputting a message, you'll want to do appropriate processing, but hopefully, you get the idea. This shows that you can (in a manner) have an array with elements of different types. Strictly speaking, this is not true, as every element is of type object (or whatever the base class in question is; you needn't go quite that far up the object hierarchy in all cases). Remember that an object of a subclass is also an object of the parent class (a Car is also a Vehicle), but the inverse is not necessarily true. Thus, there is the test to see which exact subclass the element is, in order to process it properly. If you're curious, you can also use the GetMethods(), GetMembers(), and GetProperties() methods of the System.Type class (both GetType() and typeof return a System.Type, so you can call these methods on the returned object). The last one is especially handy (it's an integral part of the mechanism through which certain data-bound controls can determine the various fields- ie, columns- to display). This page gives further details. __________________ And once again, Probability proves itself willing to sneak into a back alley and service Drama as would a copper-piece harlot. - Vaarsuvius, Order of the Stick

Jan 3rd, 2007, 7:22 PM	#2
Tim Unverified User Join Date: Dec 2006 Location: Bristol UK Posts: 19 Rep Power: 0	Do you mean you want an array that contains each of the characters form a string? Or do you want an array where each element contains a string?

Jan 3rd, 2007, 7:44 PM	#4
Tim Unverified User Join Date: Dec 2006 Location: Bristol UK Posts: 19 Rep Power: 0	My God I was being thick. It did not occur to me that that was what Arla ment. Well he could just have an array of objects. It would need some casts and would need to be managed as you need to know exactly what each element really is. Its not really an ideal solution. If you could tell us the problem you are trying to solve Arla then there might be a better way.

Jan 3rd, 2007, 7:52 PM	#5
Arla Professional Programmer Join Date: Mar 2005 Posts: 302 Rep Power: 4	Tim, Not sure I can easily explain the problem, it was more one of theories and potential ways to do something rather than "oh my word I can't possibly do this" just trying to determine optimal solutions, as such I think I've got it now, just added the required data together to make one "super" type.

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Array question