Pattern Replace Token Filter not working with "c++"

im trying to test a replace "c++" with "cplusplus" which is sopposed to be easy thing... IT IS NOT haha
what im doing is the following..
"char_filter": {
"replace_key_words": {
"type": "pattern_replace",
"pattern": "c\\+\\+",
"replacement": "cplusplus"

it works if i set c@@ ... but as soon i try to use reserved character(+ or #) i doesn't work at all, maybe there is some hiden reason why this wouldnt work, hope you guys can help me with this mistery ^^