c++ is_str_empty predicate

Question

std::vector<std::wstring> lines;
typedef std::vector<std::wstring>::iterator iterator_t;
iterator_t eventLine = std::find_if(lines.begin(), lines.end(), !is_str_empty());

how do I define is_str_empty? i don't believe boost supplies it.

Answer 1

Pure STL is enough.

#include <algorithm>
#include <functional>

...

iterator_t eventLine = std::find_if(lines.begin(), lines.end(),
                                 std::bind2nd(std::not_equal_to<std::wstring>(), L""));

Answer 2

Use boost::lambda and boost::bind and define it as bind(&std::wstring::size, _1))

Answer 3

You can use a functor:

struct is_str_empty  {
  bool operator() (const std::wstring& s) const  { return s.empty(); }
};

std::find_if(lines.begin(), lines.end(), is_str_empty());  // NOTE: is_str_empty() instantiates the object using default constructor

Note that if you want a negation, you have to change the functor:

struct is_str_not_empty  {
  bool operator() (const std::wstring& s) const  { return !s.empty(); }
};

Or just use find as suggested by KennyTM.

Answer 4

Use mem_fun / mem_fun_ref:

iterator_t eventLine = std::find_if(lines.begin(), lines.end(),
    std::mem_fun_ref(&std::wstring::empty));

If you want when the string is NOT empty, then:

iterator_t eventLine = std::find_if(lines.begin(), lines.end(),
    std::not1(std::mem_fun_ref(&std::wstring::empty)));