std::count_if为什么不能统计char元素的个数?

[ender233]

问题来源：ID 165

     vector<char> v1{'1', '.', '1'};
     const char c = '1';
     int countNum = std::count_if(v1.begin(), v1.end(), c); 
     std::cout<<countNum<<std::endl;

报错信息：

/usr/include/c++/5/bits/stl_algo.h:3193:12:   required from ‘typename std::iterator_traits<_Iterator>::difference_type std::__count_if(_InputIterator, _InputIterator, _Predicate) [with _InputIterator = __gnu_cxx::__normal_iterator<char*, std::vector<char> >; _Predicate = __gnu_cxx::__ops::_Iter_pred<char>; typename std::iterator_traits<_Iterator>::difference_type = long int]’
/usr/include/c++/5/bits/stl_algo.h:3990:29:   required from ‘typename std::iterator_traits<_Iterator>::difference_type std::count_if(_IIter, _IIter, _Predicate) [with _IIter = __gnu_cxx::__normal_iterator<char*, std::vector<char> >; _Predicate = char; typename std::iterator_traits<_Iterator>::difference_type = long int]’
count_if.cpp:14:57:   required from here
/usr/include/c++/5/bits/predefined_ops.h:234:30: error: expression cannot be used as a function
  { return bool(_M_pred(*__it)); }