c++ - Asymmetry of string::find_first_of and string::find_last_of -

c++ - Asymmetry of string::find_first_of and string::find_last_of -

with fellow member function string::find_first_of in c++ standard library can search in empty substring:

s.find_first_of(c, s.size())

or

s.find_first_of(c, string::npos)

but cannot search in empty substring string::find_last_of; next phone call search in substring containing (only) first character:

s.find_last_of(c, 0)

i think imperfection of c++ standard library, isn't it?

i don't see asymmetry here. in fact quite opposite, appears symmetrical. think of find_first_of search right starting position, while find_last_of search left starting position.

the name find_last_of has misleading quality it: implies natural forward search, except homecoming lastly occurrence instead of first one. however, bidirectional sequences 1 can ignore "forward" nature of name , think of of backward search. backward search returns first occurrence, proceeds to left starting point. point of view, function symmetrical find_first_of.

edit: after reading comments understand point. so, problem current semantics of pos parameter makes impossible specify empty search part find_last_of. yes, makes sense. agree, indeed can seen inconsistency in find_last_of design.

for consistency purposes, expect find_last_of non-inclusive respect pos value. in case specification of target position of xpos returned find_last_of be

xpos < pos , xpos < size();

in case s.find_last_of(c, 0) search empty prefix, while s.find_last_of(c, s.size()) search entire string.

however standard says

xpos <= pos , xpos < size();

i don't know why decided give pos parameter such inclusive meaning. thought create easier understand.

c++