boost::algorithm::trim_left — Left trim.
// In header: <boost/algorithm/string/trim.hpp> template<typename SequenceT> void trim_left(SequenceT & Input, const std::locale & Loc = std::locale());
Remove all leading spaces from the input. The Input sequence is modified in-place.
Parameters:
Input
An input sequence
Loc
A locale used for 'space' classification