I have encountered this kind of problem !

I dont think we could use strtok to have solution as u desire ( I dont know )

Quite an easy way to tackle is,
parse the record using the delimiter.

for ,

123, 1, ,, 45

parse the record till the end of the line delimiter
when delimiter ' , ' is encountered you have a token
when a delimiter ' , ' follows another delimiter ' , ' obviously the string would have nothing hence the purpose would be solved

Hope this helps !