Erroneous spaces when concatenating string and integer in IDL

Question

Inputting the following four lines into the IDL console gives the output below.

IDL> num=123
IDL> str="bananas"
IDL> join=str+string(num)
IDL> print,join
bananas     123

Why are 5 spaces appearing in the string and how can I stop it happening?

Answer 1

Numerical values are padded with leading blank spaces when converted with the STRING function. Use STRTRIM instead. The argument "2" removes both leading and trailing whitespace.

IDL> num=123
IDL> str="bananas"
IDL> join=str+STRTRIM(num,2)
IDL> print,join
bananas123

The STRTRIM documentation explains more about the extra spaces. This page on formatted output also has details on whitespace padding.