Abstracts: can I do better than this? - C# Discussion Boards

Re: I want to modify/replace some data from a binary file without loadig the file in memory.

#realJSOP30-Dec-09 7:08

#realJSOP

30-Dec-09 7:08

Alex Manolescu wrote:
The new data may be bigger (in size) that the replaced data!!

Then you'll have to read the entire file into memory, change the part that needs changing, and write the entire thing back out to the file again.

.45 ACP - because shooting twice is just silly
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Re: I want to modify/replace some data from a binary file without loadig the file in memory.

Alex Manolescu30-Dec-09 8:29

Alex Manolescu

30-Dec-09 8:29

Thanks you for answer!
I think my method, to read and write bytes from file to file without loading the memory, is working great for big files.

Happy New Year! Smile | :)

Re: I want to modify/replace some data from a binary file without loadig the file in memory.

Luc Pattyn30-Dec-09 6:49

Luc Pattyn

30-Dec-09 6:49

Hi,

some coding comments:

1. that continue is ugly; what you want is an if (...) ... else ...
2. please drop the flushes, they don't make any sense just before a close.
3. you can replace the close() by using a using construct.

FYI: BinaryWriter.Write(string) "Writes a length-prefixed string to this stream in the current encoding", which may or may not be what you want. And of course, inserting something in the middle of the file may break its format. Don't try it like that with an EXE file!

Smile | :)

Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles]

Merry Christmas and a Happy New Year to all.

Re: I want to modify/replace some data from a binary file without loadig the file in memory.

Alex Manolescu30-Dec-09 7:00

Alex Manolescu

30-Dec-09 7:00

Thanks you verry much for answer!
You're right about the flushes, but I am missing something at that

continue

?
Is more efficient to use a if/else statement or why is ugly?
I am just curious and I want to know Smile | :)

I've wrote a replay above yours.
Hope I've been more specific to what I want!

Cheer's,
Alex Manolescu.

Re: I want to modify/replace some data from a binary file without loadig the file in memory.

Luc Pattyn30-Dec-09 7:30

Luc Pattyn

30-Dec-09 7:30

Hi,

1.

if (br.BaseStream.Position == x) {
    // below is the data that I want to write
    bw.Write(1);
    bw.Write("StringData");
    bw.Write("StringData");
} else {
    bw.Write(b);
}

is much cleaner; performance is the same.

2.
damage to file format depends on file type. You could not do that for a Word document, an EXE file, etc.
You could do it for your own data files if your apps accept such changes.

Smile | :)

Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles]

Merry Christmas and a Happy New Year to all.

Re: I want to modify/replace some data from a binary file without loadig the file in memory.

Alex Manolescu30-Dec-09 8:25

Alex Manolescu

30-Dec-09 8:25

Thanks you for answer!
Happy New Year! Smile | :)

Re: I want to modify/replace some data from a binary file without loadig the file in memory.

petercrab30-Dec-09 17:59

petercrab

30-Dec-09 17:59

what you have written already looks ok to me. Like others have said, so long as binary file is not too large you can get a speed increase by loading entire file to memory in one read, modifying, then writing the output file.

many thanks,

petercrab

Abstracts: can I do better than this?

MollyTheCoder30-Dec-09 4:45

MollyTheCoder

30-Dec-09 4:45

I know I'm missing something simple. I have a base class, Device, and a bunch of derived classes Dev1, Dev2... Depending on the type of device active at the moment, I have an abstract method for each derived type. Deciding which to use leads me to:

if (SelectedDevice.GetType() == typeof(Dev1))
{
SetDevice((Dev1)SelectedDevice);
}
else if (SelectedDevice.GetType() == typeof(Dev2))
{
SetDevice((Dev2)SelectedDevice);
}    
else if ...

It works, but it just feels ugly.

Molly

Re: Abstracts: can I do better than this?

Luc Pattyn30-Dec-09 4:56

Luc Pattyn

30-Dec-09 4:56

rather than comparing types explicitly, you could use the is keyword.
and what is wrong with a simple SetDevice(SelectedDevice);?
or perhaps SelectedDevice.Set()?

Smile | :)

Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles]

Merry Christmas and a Happy New Year to all.

Re: Abstracts: can I do better than this?

MollyTheCoder30-Dec-09 5:22

MollyTheCoder

30-Dec-09 5:22

My apologies for using the term 'abstract' a little too loosely. The SetDevice methods control display within a form, and are not part of the Device class.

I started with SetDevice(SelectedDevice); but the compiler kicks that back because it can't be resolved at compile time.

Molly

Re: Abstracts: can I do better than this?

#realJSOP30-Dec-09 5:14

#realJSOP

30-Dec-09 5:14

You could establish an enum and then have an appropriate property in each class. Setting/getting a property probably has less impact on performance than casting.

Re: Abstracts: can I do better than this?

DaveyM6930-Dec-09 5:20

DaveyM69

30-Dec-09 5:20

I've had this problem in the past. What I decided on was to have an enum and pass the type of the device to the base classes constructor. Something like...

public enum DeviceType
{
    TypeA,
    TypeB
}

public abstract class DeviceBase
{
    private DeviceType deviceType;

    internal DeviceBase(DeviceType deviceType)
    {
        this.deviceType = deviceType;
    }

    public DeviceType DeviceType
    {
        get { return deviceType; }
    }
}

public class DeviceTypeA : DeviceBase
{
    public DeviceTypeA()
        : base(DeviceType.TypeA)
    { }
}

public class DeviceTypeB : DeviceBase
{
    public DeviceTypeB()
        : base(DeviceType.TypeB)
    { }
}

Dave

BTW, in software, hope and pray is not a viable strategy. (Luc Pattyn)
Why are you using VB6? Do you hate yourself? (Christian Graus)

Re: Abstracts: can I do better than this?

Paulo Zemek30-Dec-09 5:23

Paulo Zemek

30-Dec-09 5:23

Why can't you do something like:
SelectedDevice.Set(this)

Which Set being virtual (abstract), so the right one is called without the IF and also, if newer classes appear, you don't need to change the "Deciding" code.

Re: Abstracts: can I do better than this?

Eddy Vluggen30-Dec-09 6:56

Eddy Vluggen

30-Dec-09 6:56

MollyTheCoder wrote:
I have a base class, Device, and a bunch of derived classes Dev1, Dev2

SetDevice((Device)SelectedDevice);

This one?

I are Troll Suspicious | :suss:

Re: Abstracts: can I do better than this? [modified]

PIEBALDconsult30-Dec-09 7:20

PIEBALDconsult

30-Dec-09 7:20

Is the casting required at all? Even if SetDevice is overloaded for each type there shouldn't be a problem should there? And if not, then you still don't need to cast to each type.

Edit: I just tried it and I see the problem.

More information about SetDevice would be helpful.

And, as Luc said, use is rather than comparing types.

Edit: Or perhaps SetDevice should handle determining which type of device it was passed:

private static void
SetDev
(
    DevBase Dev
)
{
    System.Console.WriteLine ( "DevBase" ) ;

    if ( Dev is Dev1 ) SetDev ( (Dev1) Dev ) ;
    else if ( Dev is Dev2 ) SetDev ( (Dev2) Dev ) ;

    return ;
}

modified on Wednesday, December 30, 2009 2:01 PM

Re: Abstracts: can I do better than this?

MollyTheCoder30-Dec-09 7:43

MollyTheCoder

30-Dec-09 7:43

I have a form with device information for for each type of device. Most of the information is similar, so I'm sharing a single form, using SetDevice() to setup fields and controls specific to each derived device type. (right now, all SetDevice methods are inside the form, not the Device classes).

SelectedDevice is instantiated as a Device, then cast to whichever derived class is appropriate. The cast is necessary because at compile-time, SelectedDevice is just a Device, but at run-time will have a specific derived type.

Re: Abstracts: can I do better than this?

PIEBALDconsult30-Dec-09 7:52

PIEBALDconsult

30-Dec-09 7:52

I wonder whether or not dynamics in C# 4 will do it.

Re: Abstracts: can I do better than this?

MollyTheCoder30-Dec-09 7:58

MollyTheCoder

30-Dec-09 7:58

PIEBALDconsult wrote:
Or perhaps SetDevice should handle determining which type of device it was passed.

Wouldn't that mean creating a big SetDevice to handle all types, and just move the same code into SetDevice? Even if the code is a little less ugly thanks to is.

Molly

Re: Abstracts: can I do better than this?

pbalaga30-Dec-09 8:12

pbalaga

30-Dec-09 8:12

Afaik, the 'is' keyword is not fully equal to x.GetType() == typeof(y) .

Let's say I have:
class A
class B:A (B inheriting from A)

Then following (pseudo-)code:

b = new B();
b is A

returns true and

b = new B();
b.GetType() == typeof(A)

returns false.

The latter option checks for an exact type match.

Re: Abstracts: can I do better than this? [modified]

ProtoBytes30-Dec-09 8:35

ProtoBytes

30-Dec-09 8:35

Paul89 wrote:

b = new B();
b.GetType() == typeof(A);

The above test the immediate types A.GetType() != B.GetType() && B.GetType() != A.GetType()

for a better understanding try this:

b = new B();
a = new A();

typeof(A).ToString();
typeof(B).toString();

a.GetType().toString();
b.GetType().toString();

However this works like the is keyword:

B.IsSubclassOf(A) returns true

-or-

A.IsAssignableFrom(B) returns true

On the is key word:

'An is expression evaluates to true if the provided expression is non-null, and the provided object can be cast to the provided type without causing an exception to be thrown.'

modified on Wednesday, December 30, 2009 2:42 PM

Re: Abstracts: can I do better than this?

MollyTheCoder30-Dec-09 8:36

MollyTheCoder

30-Dec-09 8:36