The Wiert Corner – irregular stream of stuff

Jeroen W. Pluimers on .NET, C#, Delphi, databases, and personal interests

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Archive for the ‘C# 3.0’ Category

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Tables with SQL Server and .NET data types

Posted by jpluimers on 2013/10/23

Thanks StackOverflow users George Stocker for asking, Örjan Jämte and Sir Crispalot for answering.

Below is the SQL Server 2012 table, in which I added links to the various data types.

I also added two columns with linked references to the types from the  C# data types, C# Keywords, Reference Tables for Types (C# Reference) and Data Type Summary (Visual Basic).

One of the things I need to check is against the LINQ SQL-CLR Type Mapping.

It is very important to keep in mind that in SQL, each combination of precision and digits gets you a different decimal type, and all of them are different from the .NET decimal type. See for instance the answers on these questions:

Read the rest of this entry »

Posted in .NET, .NET 2.0, .NET 3.0, .NET 3.5, .NET 4.0, .NET 4.5, Algorithms, C#, C# 1.0, C# 2.0, C# 3.0, C# 4.0, C# 5.0, Database Development, Development, Floating point handling, Software Development, SQL Server, SQL Server 2005, SQL Server 2008, SQL Server 2008 R2, SQL Server 2012 | Leave a Comment »

.NET/C#: Type.IsSubclassOf Method versus Type.IsAssignableFrom

Posted by jpluimers on 2013/10/22

Every once in a while, you will have to do is checks using reflection.

Basically there are two methods:

Thanks to Ani and Werner Beroux for explaining the difference in more detail on StackOverflow, I added some extra links:

To check for assignability, you can use the Type.IsAssignableFrom method:

typeof(SomeType).IsAssignableFrom(typeof(Derived))

This will work as you expect for

but not when you are looking for ‘assignability’ across explicit / implicit conversion operators.

To check for strict inheritance, you can use Type.IsSubclassOf:

typeof(Derived).IsSubclassOf(typeof(SomeType))

–jeroen

via: c# – How to check if a class inherits another class without instantiating it? – Stack Overflow.

Posted in .NET, .NET 1.x, .NET 2.0, .NET 3.0, .NET 3.5, .NET 4.0, .NET 4.5, C#, C# 1.0, C# 2.0, C# 3.0, C# 4.0, C# 5.0, Development, Software Development | Leave a Comment »

.NET/C#: check for exact type: simple things are always a good solution (via: Stack Overflow)

Posted by jpluimers on 2013/10/17

A while ago, I bumped into a situation where someone had tried to solve the problem below with a convoluted reflection based solution for this seemingly simple problem:

class A {}
class B : A {}
B b = new B();
if(b is A) // this should return false

And indeed the solution is simple: replace the “b is a” with this:

b.GetType() == typeof(A)

Thanks StackOverflow users ChaosPandion and John K.

–jeroen

via c# check for exact type – Stack Overflow.

Posted in .NET, .NET 1.x, .NET 2.0, .NET 3.0, .NET 3.5, .NET 4.0, .NET 4.5, C#, C# 1.0, C# 2.0, C# 3.0, C# 4.0, C# 5.0, Development, Software Development | Leave a Comment »

A small table that shows differences between decimal, double and float (Single)

Posted by jpluimers on 2013/10/16

Though you programmers all should have read What Every Computer Scientist Should Know About Floating-Point Arithmetic.

But I know you don’t, so below is a small difference on which floating point comparisons fail when using float (f, Single), double (d) and decimal (m, money) values in C#:

0.1 fd_cast_none fd_cast_up fm_cast_none dm_cast_none
0.3 fd_cast_none fd_cast_up fm_cast_none dm_cast_none
0.7 fd_cast_none fd_cast_up fm_cast_none dm_cast_none
0.5 fm_cast_none dm_cast_none
0.9 fd_cast_none fd_cast_up fm_cast_none dm_cast_none

The can help you decide what kind of floating point type you want to use, for instance to answer c# – When should I use double instead of decimal? – Stack Overflow.

I specifically choose the values 0.1, 0.3, 0.5, 0.7 and 0.9 to stress the difference between binary and decimal representations. Apart from the decimal type, you cannot store these decimal values in a binary representation. You can see the decimal representation for a double using the DoubleConverter class (thanks Jon Skeet!)

If you are have a problem that isn’t suite for floating point, then don’t use it. Use rational types, IntX, BigInteger or Complex from the System.Numerics namespace, or arbitraty precision floating point numbers.

The failing methods are part of a bigger DecimalDoubleSingleTestProject, for which you will find the source at BeSharp.net repository (you can browse the sources, and access it through SVN and TFS).

That project contains more checks (see the table at the end which includes 0.100000000001 and 0.1222222222222222222221 based on the accuracy you can get with float/double/decimal) and the failing/succeeding methods are the same.

This is what the failing fd_cast_none, fd_cast_up, fm_cast_none and dm_cast_none methods do:

//...
    [TestClass]
    public class UnitTestBase
    {
        protected float f { get; private set; }
        protected double d { get; private set; }
        protected decimal m { get; private set; }
//...
        public void TestMethod_fd_cast_none()
        {
                Assert.AreEqual(f, d);
        }
//...
        public void TestMethod_fd_cast_up()
        {
                Assert.AreEqual((double)f, d);
        }
//...
        public void TestMethod_fm_cast_none()
        {
                Assert.AreEqual(f, m);
        }
//...
        public void TestMethod_dm_cast_none()
        {
                Assert.AreEqual(d, m);
        }
    }

The methods seem to succeed, but that is just the deceiving part: when you carefully select the values you compare, all checks will eventually fail.

The table at the end shows some more literals that fail other tests. It is caused by all these types have different storage formats.

<h3>Conclusion</h3>

When comparing floating point literals, make sure they are of the same type, and select the type according to what precision or representation features you need.

Note this gets even worse when you start calculating with floating points. You will almost always loose accuracy, watch rounding errors and you cannot even do direct AreEqual comparisons any more. Read the articles by Eric Lippert tagged floating+point+arithmetic – Fabulous Adventures In Coding.

--jeroen

Full table:

0.1 fd_cast_none fd_cast_up fm_cast_none dm_cast_none
0.3 fd_cast_none fd_cast_up fm_cast_none dm_cast_none
0.5 fm_cast_none dm_cast_none
0.7 fd_cast_none fd_cast_up fm_cast_none dm_cast_none
0.9 fd_cast_none fd_cast_up fm_cast_none dm_cast_none
0.100000000001 fd_cast_none fd_cast_up fm_cast_none fm_cast_up dm_cast_none
0.300000000003 fd_cast_none fd_cast_up fm_cast_none fm_cast_up dm_cast_none
0.500000000005 fd_cast_none fd_cast_up fm_cast_none fm_cast_up dm_cast_none
0.700000000007 fd_cast_none fd_cast_up fm_cast_none fm_cast_up dm_cast_none
0.900000000009 fd_cast_none fd_cast_up fm_cast_none fm_cast_up dm_cast_none
0.1222222222222222222221 fd_cast_none fd_cast_up fm_cast_none fm_cast_up dm_cast_none dm_cast_up
0.3222222222222222222223 fd_cast_none fd_cast_up fm_cast_none fm_cast_up dm_cast_none dm_cast_up
0.5222222222222222222225 fd_cast_none fd_cast_up fm_cast_none fm_cast_up dm_cast_none dm_cast_up
0.7222222222222222222227 fd_cast_none fd_cast_up fm_cast_none fm_cast_up dm_cast_none dm_cast_down dm_cast_up
0.9222222222222222222229 fd_cast_none fd_cast_up fm_cast_none fm_cast_up dm_cast_none dm_cast_up
144444444444444444444.1 fd_cast_none fd_cast_up fm_cast_none fm_cast_up dm_cast_none dm_cast_down dm_cast_up
344444444444444444444.3 fd_cast_none fd_cast_up fm_cast_none fm_cast_up dm_cast_none dm_cast_up
544444444444444444444.5 fd_cast_none fd_cast_up fm_cast_none fm_cast_up dm_cast_none dm_cast_up
744444444444444444444.7 fd_cast_none fd_cast_up fm_cast_none fm_cast_up dm_cast_none dm_cast_up
944444444444444444444.9 fd_cast_none fd_cast_up fm_cast_none fm_cast_up dm_cast_none dm_cast_up

Posted in .NET, .NET 1.x, .NET 2.0, .NET 3.0, .NET 3.5, .NET 4.0, .NET 4.5, Algorithms, C#, C# 1.0, C# 2.0, C# 3.0, C# 4.0, C# 5.0, Development, Floating point handling, Jon Skeet, Software Development | Leave a Comment »

.NET/C#: suffixes for compiler number literals (via: Stack Overflow)

Posted by jpluimers on 2013/10/15

A long while I avoided using suffixes to force the C# compiler into a specific type and – like Marc Gravell – used type-catst like (decimal)3.1415. I found out the hardway: it doesn’t work all the time.

(decimal)1.000000000000001 evaluates to 1 whereas
1.000000000000001m evaluates to 1.000000000000001.
In the former case, the computer parses the literal as a double and then casts it to a decimal. – Joe Albahari Apr 15 ’11 at 6:02

My main reason for using the casts was that I kept forgetting the suffixes needed to force a literal to be of a specific type. Hence this post.

The suffixes and casts are not limited to use in consts: any place where a numeric literal is used, you can use a suffix to force a compile time type.

Though documented in sections 2.4.4.2 Integer literals (C#) and 2.4.4.3 Real literals (C#) of the C# standard and appendix C. Grammar (C#). That standard does not contain a comprehensive list, much after I wrote this post I found Value Types Table (C# Reference).

This post only lists the C# suffixes. Abel Braaksma published a blog entry Overview of type suffixes in C# and VB.Net.

StackOverflow user  sixlettervariables has this (slightly) edited list:

var y = 0f; // y is single/float
var z = 0d; // z is double
var r = 0m; // r is decimal
var i = 0U; // i is unsigned int
var j = 0L; // j is long (note capital L for clarity)
var k = 0UL; // k is unsigned long (note capital L for clarity)

Some more background info: Read the rest of this entry »

Posted in .NET, .NET 1.x, .NET 2.0, .NET 3.0, .NET 3.5, .NET 4.0, .NET 4.5, Algorithms, C#, C# 1.0, C# 2.0, C# 3.0, C# 4.0, C# 5.0, Development, Floating point handling, Software Development | Leave a Comment »

.NET/C#: obtaining the full path of the process without the “.vshost” part.

Posted by jpluimers on 2013/10/08

When debugging from Visual Studio, the actual process is often the .vshost.exe one.

Visual Studio 2005 and up use to the .vshost.exe to expedite the debugging sequence startup, and enables some debugger and design-time features. This is also the reason why your bin directory is locked as soon as you open a project in Visual Studio.

You can disable this feature, but then starting the debugging sequence gets a lot slower, and you loose some security and design-time expression evaluation.

Often (for instance when your process needs to start itself multiple times) you want to have the name without the .vshost part.

There are also circumstances, where the encompassing process is not a .NET one but a native process (for instance when running under IIS, or when running an Office Add-In).

So I wrote an AssemblyHelper class that retrieves some key properties of the currently running process, be it a .NET assembly or a native process.

Part of the code was inspired by the original Delphi .NET (not Prism) run-time library.

A few notes: Read the rest of this entry »

Posted in .NET, .NET 1.x, .NET 2.0, .NET 3.0, .NET 3.5, .NET 4.0, .NET 4.5, C#, C# 1.0, C# 2.0, C# 3.0, C# 4.0, C# 5.0, Development, Software Development | Leave a Comment »

.NET/C#: When the DbDataAdapter.Update throws an exception, it is a bit tough to find the involved Command

Posted by jpluimers on 2013/09/24

When you call a DbDataAdapter.Update, and it throws an exception, the exception does not include the underlying Command and its parameters.

Since the DbDataAdapter can have three commands for applying changes (DeleteCommand, InsertCommand and UpdateCommand), asking those is a bit inconvenient.

The other way is to attach an event handler to the DAL specific RowUpdated event (for instance SqlDataAdapter.RowUpdated).

This is event is called from the virtual OnRowUpdatedMethod, and has a value parameter of type RowUpdatedEventArgs which contains the Command, and Errors that occurred. Errors is just the Exception that can help indicate what went wrong.

–jeroen

via: DbDataAdapter.Update Method System.Data.Common.

Posted in .NET, .NET 1.x, .NET 2.0, .NET 3.0, .NET 3.5, .NET 4.0, .NET 4.5, C#, C# 1.0, C# 2.0, C# 3.0, C# 4.0, C# 5.0, Development, Software Development | Leave a Comment »

.NET/C#: Igor Ostrovsky wrote a few great MSDN magazine articles helping you write better threading code

Posted by jpluimers on 2013/09/17

Igor Ostrovsky wrote a few very nice MSDN magazine articles. Not all of them have ended up in the list at MSDN magazine, so here is a more complete list:

Though the articles show the majority of sample code in C#, the actual topics are of great interest to any developer writing .NET code or interfacing to it.

Some keywords in his articles: Read the rest of this entry »

Posted in .NET, .NET 1.x, .NET 2.0, .NET 3.0, .NET 3.5, .NET 4.0, .NET 4.5, .NET CF, C, C#, C# 1.0, C# 2.0, C# 3.0, C# 4.0, C# 5.0, C++, Delphi, Development, F#, LINQ, PLINQ, Prism, Software Development, VB.NET, VB.NET 10.0, VB.NET 11.0, VB.NET 7.0, VB.NET 7.1, VB.NET 8.0, VB.NET 9.0 | Leave a Comment »

.NET/C#: Small class for double-quote escaping/unescaping (via StackOverflow)

Posted by jpluimers on 2013/09/10

Just came across this nice answer by harpo containing a small class that can Escape/Unescape double-quotes in strings.

–jeroen

via: Good CSV Writer for C#? – Stack Overflow.

Posted in .NET, .NET 1.x, .NET 2.0, .NET 3.0, .NET 3.5, .NET 4.0, .NET 4.5, C#, C# 1.0, C# 2.0, C# 3.0, C# 4.0, C# 5.0, CSV, Development, Software Development | Leave a Comment »

Visual Studio: break on all CLR exceptions, not only the unhandled ones.

Posted by jpluimers on 2013/08/29

When you have a layered exception handling (for instance to translate general exceptions into domain or business exceptions, and want to control which exceptions trickle up to where), then from a debugger perspective, most exceptions  actually handled.

However debugging those layers, it often makes sens to be able to break where all these exceptions are actually fired.

The screenshots (click on each to enlarge) are for Visual Studio 2010, but it works in any Visual Studio version and (since it is a debugger feature, not a language one) for all .NET languages I tried so far.

Note that as of Visual Studio 2010, if you disable these, it still breaks when exceptions are thrown from code called through reflection. This seems intentional and has 3 workarounds, but it might have been reverted in Visual Studio 2012.

This is a setting stored on the Solution level (.suo file) in Visual studio which by default is turned off. Luckily, it is very easy to turn this feature on, for instance for CLR (.NET Common Language Runtime) exceptions:

  1. In the “Debug” menu, choose “Exceptions” (or Press Ctrl+D, E),
  2. Wait a few moments for the dialog to appear
  3. Put a checkmark in the “Thrown” column for the “Comon Language Runtime Exceptions” row.
  4. Click the “OK” button. Read the rest of this entry »

Posted in .NET, .NET 1.x, .NET 2.0, .NET 3.0, .NET 3.5, .NET 4.0, .NET 4.5, C#, C# 1.0, C# 2.0, C# 3.0, C# 4.0, C# 5.0, Development, F#, Prism, Software Development, VB.NET, VB.NET 10.0, VB.NET 11.0, VB.NET 7.0, VB.NET 7.1, VB.NET 8.0, VB.NET 9.0 | 1 Comment »

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