Ben Nadel
On User Experience (UX) Design, JavaScript, ColdFusion, Node.js, Life, and Love.
I am the chief technical officer at InVision App, Inc - a prototyping and collaboration platform for designers, built by designers. I also rock out in JavaScript and ColdFusion 24x7.
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Ben Nadel at CFUNITED 2010 (Landsdown, VA) with:

ColdFusion Bug: Arrays, ArrayLen(), And Implicit Structs

By Ben Nadel on
Tags: ColdFusion

I just ran up against a strange bug using ColdFusion arrays and implicit structs. I have experienced and read about several issues with implicit structs before and I would bet that this bug is falling under the same mechanism. The error occurs when I try to create an implicit struct and add it to an array at the same time. However, the bug only occurs if I get the array index of the insert based on the existing length of the array:

  • <!--- Define array. --->
  • <cfset arrData = [] />
  •  
  • <!--- Add struct to array. --->
  • <cfset arrData[ ArrayLen( arrData ) + 1 ] = { Foo = "Bar" } />

This throws the ColdFusion error:

The element at position 2 of dimension 1, of array variable "ARRDATA," cannot be found.

At first, I thought maybe there was something wrong with my indexing math; but, if you separate the calculation out into a separate line:

  • <!--- Define array. --->
  • <cfset arrData = [] />
  •  
  • <!--- Get next index. --->
  • <cfset intIndex = (ArrayLen( arrData ) + 1) />
  •  
  • <!--- Add struct to array. --->
  • <cfset arrData[ intIndex ] = { Foo = "Bar" } />

... it works just fine. I know I just read something recently on the order of operations that gets carried out with implicit structs, but I am not sure that this applies here as the error seems to be a function of the ArrayLen() evaluation.




Reader Comments

In addition to your second example actually working, I believe it is also more readable. I find this to be a better coding standard - one I try to follow, at least in other scripting languages. It is similar to looping over the length of an Array.

I would prefer this:

<cfset myArrayLen = ArrayLen(myArray) />

<cfloop from="1" to "#myArrayLen#" index="i">
....
</cfloop>

to this:

<cfloop from="1" to "#ArrayLen(myArray)#" index="i">
....
</cfloop>

Reply to this Comment

@Eric,

Ideally, what I would like to do is actually pass the implicit struct to the ArrayAppend() method:

<cfset ArrayAppend( arrData, { Foo = "Bar" } ) />

... but ColdFusion cannot support this yet. Hopefully in CF9, this improvement will be there. I think it's the best of both worlds.

Reply to this Comment

Hmm, for what you're doing there in the example, wouldn't it make more sense to use ArrayAppend()?

I'm not surprised CFML couldn't handle something like that. Have you tried the same code in CFScript? Somehow I think CFScript will work...

Reply to this Comment

Here's something weird:
<cfset arrData[ ArrayLen( arrData ) + 1 ] = "">

Does work for me, it's only when passing an implied structure that throws it off.

For me I use a simple function to get around this which also works as seen here:

<cffunction name="Echo" access="public" returntype="any" output="false" hint="Just returns the arguments passed to it.">
<cfreturn ARGUMENTS />
</cffunction>
<!--- Define array. --->
<cfset arrData = []>

<!--- Get next index. --->
<cfset arrData[ ArrayLen( arrData ) + 1 ] = Echo(Foo="Bar")>

Reply to this Comment

@Henry,

I have not tried this in Script, but I think it's a compile time error, not a runtime error. So, it may work in script, not sure.

@Tim,

Yeah, its a strange error. Implicit creation must be doing something rather odd.

Reply to this Comment

This is the same bug that I've blogged about several times. ColdFusion compiles this code:

<cfset a[arrayLen(a) + 1] = { foo = 2 } />

into this:

<cfset a[arrayLen(a) + 1] = structNew() />
<cfset a[arrayLen(a) + 1].foo = 2 />

This is a bug in ColdFusion's processing of struct literals, nothing to do with arrays. If you execute that code on Railo it'll work just dandy.

Reply to this Comment

@Barney,

Ahhh, you were the one who blogged about it! For some reason I thought it was Elliott Sprehn (I tried Googling it when it happened). Thanks for the clarification.

Reply to this Comment

Hi Ben,

I think you're right, it is a bug. It looks like the array is trying to reference the array at zero.

Try this code:

<cfset arrData = ['']>
<cfset arrData[(arrayLen(arrData)+1) - 1 ] = { Foo = "Bar" }>

<cfdump var="#arrData#"><cfabort>

Reply to this Comment

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