Regular expression - vim matchstr() cannot match the number in :4:

Question

let a=['','']
echo matchstr(get(a,0),"[0-9] \+")
echo matchstr(get(a,1),"\d\+")
all display empty string

:s/\d\+/xxx/cg
can match 4
but the {pat} in matchstr() is unsuccessful!

Answer 1

Brother upstairs, the first suggestion is correct. echo matchstr(get(a,0),"[0-9]+")It is indeed empty, there is no problem

Answer 2

I haven’t written it before, but I feel it is a problem with "". It is recommended to try:
1. Two \ For example: "[0-9]\+"
2. Remove For example: "[0-9]+"