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I have used find_if before with lists and vectors in C++ and it has worked fine. But now, when I try to use it with sets I get the following error: 

 error: no matching function for call to ‘find_if(std::set<A, Acmp>::iterator, 
 std::set<A, Acmp>::iterator, <unresolved overloaded function type>)’|

My class is the following:

bool searchForA(A i) {
   return (i.getVal() > 0);
 }


void B::findA()
 {
   set<A, Acmp> cont;
   set<A, Acmp>::iterator it;
   A *a1 = new A(5);
   A *a2 = new A(7);
   cont.insert(*a1);
   cont.insert(*a2);

   it = find_if (cont.begin(), cont.end(), search)
}

Can anyone help me understand where is the problem?

hivert
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FranXh
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  • No I have not included that inside class A for the set. IF I may ask, why would overloading < affect find_if? – FranXh Mar 06 '13 at 04:42
  • How about declaring `search (A const &i)` – Mark Taylor Mar 06 '13 at 04:44
  • That's a lovely way to leak memory. The pointers are completely unnecessary. By the way, [this](http://liveworkspace.org/code/3v0m5c%247) is close and works. – chris Mar 06 '13 at 04:45
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    set element needs to be weak ordered, try to add `operator<` your code should compile, also as chris mentions, your code leaks memory – billz Mar 06 '13 at 04:46
  • Is the definition of the `search()` function you gave above exactly the same as in your code? And is it the only definition for that function, or are there any overloads? – jogojapan Mar 06 '13 at 04:46
  • Ok, so I changed the name of the function, and I added to the set a Comparator. I will take care of the pointers too. – FranXh Mar 06 '13 at 04:49
  • Sorry I take that back. Apparently the name of the function was the problem. – FranXh Mar 06 '13 at 04:50
  • @billz The OP apparently uses a customised comparator `Acmp` for the set. So, adding a `operator<` won't change anything. Also, the comparison operator isn't relevant when `find_if` is used. – jogojapan Mar 06 '13 at 04:55
  • @jogojapan yeah, looks like it. I think Dave's answer is on the right direction. – billz Mar 06 '13 at 04:58

2 Answers2

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There's already a function in the STL called search. That's probably why the compiler can't resolve the right name without a better hint. You could rename your search function. Or if you don't want to do that, try passing ::search into find_if instead.

Dave Johnson
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  • That's what I thought initially too. I tried to change the name of the function. Still the same error. – FranXh Mar 06 '13 at 04:42
  • No, changing the name of the function does fix that error. You're getting another big error because A needs a comparison operator, like the other people said. – Dave Johnson Mar 06 '13 at 04:50
  • Yes changing the name fixed the problem. – FranXh Mar 06 '13 at 04:51
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There is more than one function named search — the name is overloaded. To pass a pointer to search into find_if, you need to specify which one. The most straightforward way is to specify static_cast< bool (*)( A ) >( cont ).

Potatoswatter
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