getFileType

Last week I showed you how to get the size of a file. This week I'm going to show you how to get the type of a file. This is useful if you want to display an icon or bit of text next to a hyperlink to indicate the file type. Some people like to use this to warn visitors when they link to a PDF file, because PDF readers can take a while to load.

ASP

1. function getFileType(someFile)
2.     dim fs
4.     set fs = Server.CreateObject("Scripting.FileSystemObject")
5.     getFileType = fs.GetExtensionName(Server.MapPath(someFile))
6.     set fs = nothing
7. end function

See you next week!

View ASP implementation on Snipplr

getFileSize

When you provide a link to a file for the user to download, it's sometimes nice to provide the size of the file so that they know what they're getting themselves into.

ASP

1. function getFileSize(someFile)
2.     dim fs
3.     dim file
5.     set fs = Server.CreateObject("Scripting.FileSystemObject")
6.     set file = fs.GetFile(Server.MapPath(someFile))
8.     getFileSize = FormatFileSize(file.size)
9.     set file = nothing
10.     set fs = nothing
11. end function

The size property returns the size in bytes, which could be a very large number. As you may have guessed, we're going to write a FormatFileSize function to wrap around it.

ASP

1. function FormatFileSize(size)
2.     dim units
3.     dim factor
5.     units = Array("B", "kB", "MB", "GB", "TB", "PB", "EB", "ZB", "YB")
6.     factor = log(size) \ 7
8.     FormatFileSize = Round(size / (1024 ^ factor), 2) & units(factor)
9. end function

I think it will be a very, very long time before we reach yottabytes, so this function should withstand the test of time. Next week I'll show you how to get the file type and why you might want that.

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Soundex

This week we're going to write a function to convert letters to their corresponding soundex codes. But wait, there's more! We'll also allow you to pass in an entire string and convert the whole thing. Here's the set up:

1. function soundex(someString)
2.     if len(someString) = 1 then
3.         ' code to convert a single character
4.     else
5.         ' loop through the whole string and convert each character
6.     end if
7. end function

Inside the loop, we'll recursively call the soundex function to convert the individual character. Actually, this may not perfectly fit the definition of recursion. The only recursive aspect of it is that the function calls itself, but an entirely different execution path is being followed once inside. But that's good, because we won't have the poor performance that sometimes comes with recursion.

Once again, the full source code is a little too long to post, so you'll have to grab it from Snipplr:

• View ASP implementation on Snipplr
• View PHP implementation on Snipplr

Luhn Algorithm

This week we're writing a function to verify credit card numbers. Credit cards have a check digit which is generated with the Luhn algorithm. The code is too long to post here, but as always it is posted on Snipplr and linked here for your dissemination.

• View ASP implementation on Snipplr
• View PHP implementation on Snipplr

Phonetic Alphabet

It seems to me that most people have trouble remembering the phonetic alphabet (probably myself included). Unless you're a pilot or air traffic controller, it's unlikely that your job requires you to have it memorized. People get by with whatever word comes to mind ("A as in Adam"), but this seems like an opportunity to write some code.

For maximum reusability, I'm going to write my function to convert individual characters at a time. Looping through the characters of the string will occur outside the function. The function is too long to paste here in its entirety, but it will be posted on Snipplr and linked at the bottom of this entry.

PHP has key/value arrays where we can specify any keys we want, so we'll declare an array containing all the conversions and use the input to retrieve the correct string from the array. ASP's arrays don't have this flexibility; we could achieve this with a Dictionary scripting object, but I'm concerned about the overhead associated with that. I'm going to use a Select...Case statement (AKA switch statement), but there is a chance that this is actually not any better. I'll leave the determination of this as an exercise to the reader. Also left as an exercise to the reader is the writing of the looping code.

• View ASP implementation on Snipplr
• View PHP implementation on Snipplr

Add and strip slashes

Good programmers know that they can't trust user-inputted data. We do as much as we can to validate and try to prevent bad data from getting into our applications. But there is even some perfectly valid data that can cause trouble, especially when you're dealing with databases. The single apostrophe is a common occurrence and gotcha for the newbies when they discover the tail end of their string didn't make it into the database.

Our PHP programmer friends have a few different functions at their disposal. Native to PHP are the addslashes() and stripslashes() functions, which basically do what they say. In more common usage these days is the MySQL-native function, mysql_real_escape_string(), which can handle a wider variety of situations. I'm going to go a little bit further and handle the backspace and horizontal tab characters.

The regular expression we'll be using to add slashes is ([\000\010\011\012\015\032\042\047\134\140]), and to remove slashes we'll use \\([\000\010\011\012\015\032\042\047\134\140]). The only difference is the extra pair of slashes at the beginning. These handle, respectively: null, backspace, horizontal tab, new line, carriage return, substitute, double quote, single quote, backslash, and grave accent.

• View ASP implementation on Snipplr.
• View VB.NET implementation on Snipplr

htmlspecialchars()

If you rigoursly validate your HTML like I do, you've probably seen many times the warning about HTML entities. Inevitably an ampersand makes its way into your code without being properly encoded. It's almost always in a hyperlink where you're trying to pass a QueryString variable or two.

somefile.asp?this=that&blah=meh

That ampersand needs to be encoded as &. Likewise, double quotation marks need to be encoded as " and the greater than and less than symbols need to be encoded as > and < respectively. If you allow users to write things on your web site, then you need a programmatic solution. Our PHP programmer friends have one in their toolbox which we can borrow.

1. function htmlspecialchars(someString)
2.     ' Critical that ampersand is converted first, since all entities contain them.
3.     htmlspecialchars = replace(replace(replace(replace(someString, "&", "&"), ">", ">"), "<", "<"), """", """)
4. end function
6. function htmlspecialchars_decode(someString)
7.     htmlspecialchars_decode = replace(replace(replace(replace(someString, "&", "&"), ">", ">"), "<", "<"), """, """")
8. end function

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