Can't pass file name as parameter to Corpus function

I'm working on a small project to extract high-frequency terms from a
document and then display those terms in web page. To this end, I've to pass
the file name as parameter to the Corpus function to build a corpus of only
one document. I can build the corpus using the code below interactively in
R. But calling the function with a file name as the parameter I got the
error message saying "Error in eval(expr, envir, enclos) : object
'strFileName' not found"

test<-function(strFileName) {
	src <- URISource(strFileName)
	cor <- Corpus(src, readerControl = list(reader = readPDF, language =
"en_US", load = TRUE))
}

After running the following code in R I checked the docURISource$URI and the
value is "strFileName" rather than "C:\\Temp\\readme.txt". I also checked
the URI when I was debugging the function and the URI is also  "strFileName"
rather than "C:\\Temp\\readme.txt". 

strFileName <- "C:\\Temp\\readme.txt"
docURISource = URISource(strFileName, encoding = "UTF_8")
docCorpus = Corpus(docURISource)

So it seems when running interactively the URI contains strFileName as a
variable but when called as a function, the URI contains strFileName as the
actual value. Can anybody point out what's the problem?

thanks in advance!!

Jianli