and why you are not using StringUtils library? i mean there is a printf function in there and i guess it has the same functionality. the thing is that IECStringUtils is not even documented well in CODESYS Online Help. i am working on a brandlabeled version of CODESYS (KeStudio from Company KEBA) and in this version the IECStringUtils is not included. would it be a problem for you to change the library?
IECStringUtils