CODEWITHSUNDEEP
c++templatesstaticcompiler-errors
F. P.
F. P.

Reputation: 5086

Template Issues - Having trouble passing function as args (invalid use of non-static member function)

Here's a template I made. I believe it is self-explanatory

   template <class N, class I>
    std::list<N*> selectiveList(I element, std::list<N*> & container, I (N::*f)() const) {
 typename std::list<N*>::iterator it;

 std::list<N*> selectiveListing;

 for (it = container.begin(); it != container.end(); ++it)
  if ((*it)->*f == element)
   selectiveListing.push_back(*it);

 if (selectiveListing.size() == 0)
  throw NoItemsFound<I>(element);

 return selectiveListing;
}

I call it from this function:

void AirportManager::searchAirplanesTypes() {
 clrscr();
 std::stringstream prompt;
 prompt  <<  "Escolha atributo a pesquisar: \n" <<
    "1) Tipo\n" <<
    "2) Descricao\n" << "3) Categoria\n";

 int choice = getNumberInput(prompt.str(), 1, 3);

 switch (choice) {
 case 1: {
  std::string searchElement1 = getStringInput("Tipo: ");
  pageNav(selectiveList(searchElement1, airport.airplanesTypes,
    &AirplaneType::getType), "", true, true);
  break;
 }
 case 2: {
  std::string searchElement2 = getStringInput("Descricao: ");
  pageNav(selectiveList(searchElement2, airport.airplanesTypes,
    &AirplaneType::getDescription), "", true, true);
  break;
 }
 case 3: {
            //Category is an enumerated data type
  Category searchElement3 = getCategoryInput("Categoria: ");
  pageNav(selectiveList(searchElement3, airport.airplanesTypes,
    &AirplaneType::getCategory), "", true, true);
  break;

 }
 }
}

I really can't see anything wrong. Yet when I compile it, here's what happens:

In file included from ..\src\AirportManager.cpp:14:0:
..\src\/headers/Template.h: In function 'std::list<N*> selectiveList(I, std::list<N*>&, I (N::*)()const) [with N = AirplaneType, I = std::basic_string<char>]':
..\src\AirportManager.cpp:1259:34:   instantiated from here
..\src\/headers/Template.h:340:3: error: invalid use of non-static member function
..\src\/headers/Template.h: In function 'std::list<N*> selectiveList(I, std::list<N*>&, I (N::*)()const) [with N = AirplaneType, I = Category]':
..\src\AirportManager.cpp:1265:31:   instantiated from here
..\src\/headers/Template.h:340:3: error: invalid use of non-static member function

These are a bit random. I can't see how statics come into play here. All the getters referenced are simple const returns.

I'd be happy to get some input.

Upvotes: 0

Views: 404

Answers (3)

wilhelmtell
wilhelmtell

Reputation: 58677

The canonical way to copy elements is to use a negated std::remove_copy_if() or write a copy_if() algorithm. IMHO copy_if() is the clearer alternative, and eventhough it is not a standard function it is very easy to write properly:

template<class In, class Out, class Pred>
Out std::copy_if(In first, In last, Out res, Pred p)
{
    while( first != last ) {
        if( p(*first) ) *res++ = *first;
        ++first;
    }
    return res;
}

You can then use it like so:

if( choice == 1 ) {
    copy_if(airport.airplanesTypes.begin(), airport.airplanesTypes.end(),
            std::back_inserter(result),
            boost::bind(&AirplaneType::getType, _1, searchElement1));
    pageNav(result, "", true, true);
} else if( choice == 2 ) {  // ...

The nice thing here is that you can use copy_if() for plenty of other things. It works with any container, not just std::list<N*> and it works with any unary predicate, whether a primitive function or a function object.

Upvotes: 1

Hogan
Hogan

Reputation: 70523

It has been a while, but are you missing a new?

throw new NoItemsFound<I>(element);

Upvotes: 0

usta
usta

Reputation: 6869

if (((*it)->*f)() == element)

Upvotes: 2

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