Failing To Use Array of Structure in C#

Question

I am sorry for the weird title but I coulnt figure out how to express it :) I recently shifted to C# and currently I am working on structures. I am basically a C++ developer and in my c++ code I had done the folowing:

typedef struct 
{
String ChannelName;
bool available;
} Voltage_Channel;

Voltage_Channel *m_voltageChannels;

Voltage_Channel redhookChannels[6] = {
{"", false},
{"VDD_IO_AUD",  true},
{"VDD_CODEC_AUD",true},
{"VDD_DAL_AUD", true},
{"VDD_DPD_AUD",  true},
{"VDD_PLL_AUD", true}   
};

if(m_boardName->compareIgnoreCase("S1010012") == 0) //m_BoardName is string
{   
    m_voltageChannels = redhookChannels;
}

I need to do this in my c# application. I tried it as follows but something is wrong:

struct VoltageBoardChannel
    {
        public string ChannelName;
        public bool available;            
    };

VoltageBoardChannel[] mVoltageStruct; 

VoltageBoardChannel[] redhookChannels = new VoltageBoardChannel[6]
    {
        new VoltageBoardChannel() { ChannelName = "", available = false},
        new VoltageBoardChannel() { ChannelName = "VDD_IO_AUD", available = true},
        new VoltageBoardChannel() { ChannelName = "VDD_CODEC_AUD", available = true},
        new VoltageBoardChannel() { ChannelName = "VDD_DAL_AUD", available = true},
        new VoltageBoardChannel() { ChannelName = "VDD_DPD_AUD", available = true},
        new VoltageBoardChannel() { ChannelName = "VDD_PLL_AUD", available = true}            
    };

string redhookboardname = "S1010012";
string redhookboardnameCase = "s1010012";

if (redhookboardnameCase.Equals(redhookboardname, stringComparison.InvariantCultureIgnoreCase))
        {
            mVoltageStruct = redhookChannels;
        }

Where Am I making a mistake??? :(

What are you trying to assign mVoltageStruct ? do you want to assign the first item of your array redhookChannels ? — Habib
– Habib, Commented Oct 12, 2012 at 6:02
I want to assign all values of redhookChannels to mVoltageStruct — StonedJesus
– StonedJesus, Commented Oct 12, 2012 at 6:07
@StonedJesus but what does that mean? For example: you have a variable that can hold a single "person", and a list of 6 "people"; how do you assign the values of all 6 "people" to the single "person" variable? It looks to me like m_voltageChannels is a pointer to the first item in the array, but that isn't copying anything. — Marc Gravell
– Marc Gravell, Commented Oct 12, 2012 at 6:08
well mVoltageStruct is a single item struct, and your redhookChannels is an array, in your C++ code you are assigning it to a pointer of the struct type, In C# you have define another array and make copy of it. — Habib
– Habib, Commented Oct 12, 2012 at 6:09
@Habib you don't have to do that at all; the correct next step depends a lot on what you want to do with it, and how you want to behave. Making a copy of the array will significantly change the behaviour, for example if we change values via the pointer, are the array contents updated? — Marc Gravell
– Marc Gravell, Commented Oct 12, 2012 at 6:11

Marc Gravell · Accepted Answer · 2012-10-12 06:23:01Z

1

mVoltageStruct is an individual value; redhookChannels is an array. You can't assign an array to a value. You can, however, peek inside the array:

mVoltageStruct = redhookChannels[0]; // copy the item with index 0, zero-based

Note, however, that unless you have specific reasons (P/Invoke etc) to use a struct, you might want to consider using a class there. Mutable structs usually cause a lot of confusion. struct in C# does not mean the same as struct in C/C++.

Note also that the line mVoltageStruct = redhookChannels[0]; is a copy operation; it does not mean that mVoltageStruct is a reference / pointer to the zeroth item. There are ways to do that in C#, but it would be a lot easier if you were using a class; then you would be only copying the reference-value.

Edit per comments:

using System;
using System.Collections.Generic;
class VoltageBoardChannel
{
    public string ChannelName { get; set; }
    public bool IsAvailable { get; set; }
}
static class Program {
    static void Main()
    {
        List<VoltageBoardChannel> selectedChannels = null;

        List <VoltageBoardChannel> redhookChannels = new List<VoltageBoardChannel>
        {
            new VoltageBoardChannel { ChannelName = "", IsAvailable = false},
            new VoltageBoardChannel { ChannelName = "VDD_IO_AUD", IsAvailable = true},
            new VoltageBoardChannel { ChannelName = "VDD_CODEC_AUD", IsAvailable = true},
            new VoltageBoardChannel { ChannelName = "VDD_DAL_AUD", IsAvailable = true},
            new VoltageBoardChannel { ChannelName = "VDD_DPD_AUD", IsAvailable = true},
            new VoltageBoardChannel { ChannelName = "VDD_PLL_AUD", IsAvailable = true}            
        };

        string redhookboardname = "S1010012";
        string redhookboardnameCase = "s1010012";

        // string.Equals(a,b,...) rather than a.Equals(b, ...) avoids
        // potential issues when "a" is null
        if (string.Equals(redhookboardnameCase, redhookboardname,
            StringComparison.InvariantCultureIgnoreCase))
        {
            // set selectedChannels to the **same** list:
            selectedChannels = redhookChannels;

            // or if we wanted a filtered list (same VoltageBoardChannel
            // objects, but a different list instance)
            selectedChannels = redhookChannels.FindAll(x => x.IsAvailable);
        }
    }
}

edited Oct 12, 2012 at 6:23

answered Oct 12, 2012 at 6:04

Marc Gravell

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10 Comments

StonedJesus Over a year ago

Thanks :) I need to copy all items in mVoltageStruct. Hows that possible?

Marc Gravell Over a year ago

@StonedJesus why do you need to copy all the values? Is that really what the original code does? Where would you put them? (you haven't declared a second array, etc)

StonedJesus Over a year ago

I need to copy all the channels to display in my view. I will be using channelname.available function later to make only true items visible in my view :)

Marc Gravell Over a year ago

@StonedJesus I disagree; since an array has fixed size, making an additional copy doesn't help you at all; it certainly won't help you include/exclude specific rows. And it is different to what the original code does/did.

StonedJesus Over a year ago

Yes you are right. Then what's the ideal way of doing it? Can u post a sample Code to demonstrate using a class?

|

cuongle · Accepted Answer · 2012-10-12 06:07:17Z

1

What you need is just to declare mVoltageStruct as Array, not an object:

  VoltageBoardChannel[] mVoltageStruct;

Then you can assign:

 if (redhookboardnameCase.Equals(redhookboardname, StringComparison.InvariantCultureIgnoreCase))
 {
       mVoltageStruct = redhookChannels;
 }

answered Oct 12, 2012 at 6:07

cuongle

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1 Comment

Marc Gravell Over a year ago

pedantic point; mVoltageStruct is at no point "an object"; it probably doesn't matter in regular discussion, though

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