Arrays of Function Pointers in C++

So imagine you have a function called test_function_ref in a class called DLMAP. In another function in the same class, you want to have an array of function pointers that includes test_function_ref, and then you want to call it using the array of function pointers. This is how you would do that:

void (DLMAP::*fptr[2])(BitStream &theBits);
// set up an array of functions that return void and take a reference
// to a BitStream object as an argument
fptr[1] = &DLMAP::test_function_ref;
// assign the 1'th element of the function pointer array to the address of the function
(*this.*fptr[1])(theBits);
// now, actually call the function using the this pointer


Wasn't that fun? I got the info here.

XPath, C#, .NET, and namespaces.

So I was trying to use XPath to search this XML document I'm working with using System.Xml in C#/.Net. The obvious thing to use for me was the method SelectSingleNode(). I had read around that you had to be very careful with default namespaces using XPath 1.0 in .Net. In summary, all namespaces must have a prefix, even the default one. You just have to make a prefix up for the default namespace. I chose the imaginative "default" prefix.

Anyway, these were the first couple lines of my XML doc:


<?xml version="1.0" encoding="utf-8"?>
<Specification Standard="802.16e Cor2, 2007" VersionDate="2007-06-21" Company="Sanjole Inc." Author="Min Xu" xmlns="http://sanjole.com/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:msxsl="urn:schemas-microsoft-com:xslt" xsi:schemaLocation="http://sanjole.com/ Sanjole.xsd">


So I have a default namespace. I used the following code, which didn't work:

XmlDocument xmlSpecDoc = new XmlDocument();
xmlSpecDoc.Load(xmlSpecFileName);
XmlNamespaceManager nsmgr = new XmlNamespaceManager(xmlSpecDoc.NameTable);
nsmgr.AddNamespace("default", "http://sanjole.com");
nsmgr.AddNamespace("xsi", "http://www.w3.org/2001/XMLSchema-instance");
nsmgr.AddNamespace("xsl", "http://www.w3.org/1999/XSL/Transform");
nsmgr.AddNamespace("msxsl", "urn:schemas-microsoft-com:xslt");
XmlElement root = xmlSpecDoc.DocumentElement;
XmlNode messageNode = root.SelectSingleNode("/default:Specification", nsmgr);


This returned a messageNode of null, even though it's obviously in the document.

Can you find the bug? Me neither, but my colleague found it... look closely at the default namespace. Give up? It should have been:

nsmgr.AddNamespace("default", "http://sanjole.com/");

That's right... watch your trailing "/"'s. I'm won't reveal how long I was messing with this. Let's just say it was in the range of "hours".

Tales of Irony

Recently, I purchased a pair of fabric scissors. They came in a blister pack.

I sent the company an email:


Dear Sir or Madam,

I recently purchased a pair of Helping Hand Fabric Scissors. Ironically, these scissors are packaged in a "blister pack", which to open, you actually need a pair of scissors. I would like to suggest that you find an alternative means of packaging scissors that don't require scissors to open.

Thank you for your attention to this matter.

Sincerely,
David A. Donovan


I really hope they listen.