Using find_if on a vector of objects

Question

I am not using boost libraries. How can i do this using STL?

class Files
{

private:
   bool isSame(FileID f1, FileId f2)
   { 
      if(f1.getId()==f2.getId())
        return true;
      return false;
   }

public:
   vector<FileId> mod_files;

    void update()
    {
      FildId f = getFileId();
      vector<FildId>::const_iterator found = find_if(mod_files.begin(), mod_files.end(),          ???);
    }

};

I would like to pass isSame as the third argument to find_if function, and bind "f" to the isSame's second argument.

I think you want your private and public switched. that way you can call "isSame" from outside the class. — Trevor Hickey
– Trevor Hickey, Commented Jun 19, 2012 at 1:57

K-ballo · Accepted Answer · 2012-06-19 02:05:36Z

4

In C++11 that's simply:

std::bind(&Files::isSame, this, f);

In good old C++03 there is no mem_fun that takes 2 arguments, so you would have to do the binding on your own:

class is_same_pred
{
public:
    // unary function typedefs

    explicit is_same_pred(Files& files, FileId f1) : _files(files), _f1(f1) {}

    bool operator()(FileId f2) const { return _files.isSame(_f1, f2); }

private:
    Files& _files;
    FileId _f1;
};

Where isSame is accessible to is_same_pred, and later use it like this:

is_same_pred(this, f);

All that said and done, you would be better off defining isSame as a static or free-function:

bool isSame(FileId f1, FileId f2){ ... }

std::bind1st(std::ptr_fun(&isSame), f);

answered Jun 19, 2012 at 2:05

K-ballo

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2 Comments

stinky472 Over a year ago

Just to throw in my two cents, I think once we get to writing our own predicates or trying to do things with bind1st, mem_fun, etc.: it's time to consider letting go of find_if and just writing a simple old vanilla search loop which everyone is used to doing. Unless we have the tools (C++11/boost, e.g.) and experience necessary so that generic algorithms flow freely and naturally from our fingertips, I think they should be avoided. If it's giving us headaches to write it in the first place, most people probably wouldn't want to debug it.

stinky472 Over a year ago

+1 for pointing out that isSame has no benefits being a non-static method, and I wish I could give another +2 for pointing out that what he wants to do exactly as he's doing it is impossible in C++03 using just mem_fun (nullary to unary, not binary to ternary) and STL binders

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