CODEWITHSUNDEEP
c++
FranXh
FranXh

Reputation: 4771

C++ find_if function:

I am trying to understand how the find_if function works, and I am following the example in this reference:

http://www.cplusplus.com/reference/algorithm/find_if/

When I follow the example given in the above reference, meaning when I use main(), everything works fine. But when I try to include that example inside a class (as I have shown below) I get this error when I compile:

error: argument of type ‘bool (A::)(int)’ does not match ‘bool (A::*)(int)’

Inside my class:

 bool A::IsOdd (int i) {
  return ((i%2)==1);
}


void A::function(){
   std::vector<int> myvector;

   myvector.push_back(10);
   myvector.push_back(25);
   myvector.push_back(40);
   myvector.push_back(55);

   std::vector<int>::iterator it = std::find_if (myvector.begin(), myvector.end(), IsOdd);
   std::cout << "The first odd value is " << *it << '\n';
  }

Can anyone help me understand why this is happening?

Upvotes: 1

Views: 772

Answers (1)

Zeta
Zeta

Reputation: 105886

A::isOdd needs to be a static method. Otherwise it can only be used in conjunction with a specific A. Since isOdd doesn't depend on member fields at all it is save to change it into a static method. Even more, since it doesn't depend on the class at all, you can just create a global isOdd:

bool isOdd(int i){
    return i % 2;
}

EDIT: As suggested by chris, you can also use a simple lambda (C++11):

auto it = std::find_if (
     myvector.begin(), 
     myvector.end(),
     [](int i) -> bool{ return i % 2; }
);

Upvotes: 5

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