Using find_if on a vector of object

That’s not how predicates work. You have to supply either a free function bool Comparator(const MyClass & m) { ... }, or build a function object, a class that overloads operator():

struct MyClassComp
{
  explicit MyClassComp(int i) n(i) { }
  inline bool operator()(const MyClass & m) const { return m.myInt == n; }
private:
  int n;
};

std::find_if(v.begin(), v.end(), MyClassComp(5));

In C++0x:

std::find_if(v.begin(), v.end(),
             [](const MyClass & m) -> bool { return m.myInt == 5; });

This captureless lambda is in fact equivalent to a free function. Here is a capturing version that mimics the predicate object:

const int n = find_me();
std::find_if(v.begin(), v.end(),
             [n](const MyClass & m) -> bool { return m.myInt == n; });