Question

I am trying to remove short strings from a vector.

std::vector<std::string> vec;

// ...

vec.erase(std::remove_if(vec.begin(),
                         vec.end(),
                         boost::bind(std::less<size_t>(),
                                     boost::bind(&std::string::length, _1),
                                     5),
          vec.end());

The compiler spits out a very large error message:

qwer.cpp:20: error: no matching function for call to 'remove_if(__gnu_cxx::__nor
mal_iterator<std::basic_string<char, std::char_traits<char>, std::allocator<char
> >*, std::vector<std::basic_string<char, std::char_traits<char>, std::allocator
<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::al
locator<char> > > > >, __gnu_cxx::__normal_iterator<std::basic_string<char, std:
:char_traits<char>, std::allocator<char> >*, std::vector<std::basic_string<char,
 std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_strin
g<char, std::char_traits<char>, std::allocator<char> > > > >, boost::_bi::bind_t
<boost::_bi::unspecified, std::less<unsigned int>, boost::_bi::list2<boost::_bi:
:bind_t<unsigned int, boost::_mfi::cmf0<unsigned int, std::basic_string<char, st
d::char_traits<char>, std::allocator<char> > >, boost::_bi::list1<boost::arg<1>
> >, boost::_bi::value<int> > >, __gnu_cxx::__normal_iterator<std::basic_string<
char, std::char_traits<char>, std::allocator<char> >*, std::vector<std::basic_st
ring<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::b
asic_string<char, std::char_traits<char>, std::allocator<char> > > > >)'

The following solution works:

vec.erase(std::remove_if(vec.begin(),
                         vec.end(),
                         boost::bind(&std::string::length, _1) < 5),
          vec.end());

But I am still curious as to what I did wrong in the first version. Thanks!

Answer 1

It looks like you got your parenthesis off (there should be two after 5, one to close the bind, one to close the remove_if.) I am surprised this didn’t give another error message about invalid token or something though, as the parens are clearly unbalanced (did you remove an extra close paren from the end while preparing for SO?). It looks like this is the case, because if you read the template arguments to remove_if in the error message, the next to last one is a boost bind_t, followed by another gnu::iterator.