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Stl :: find_if with user find

I was wondering if there is a way to use stl :: find_if to find a user-entered value

I don't know how to do this without using any bad conventions (globals) or adding loads of extended code.

For example, if the user enters int x for 10, then I want to search for the vector ints

iterator = find_if(begin,end,pred) //but how does pred know the user inputted value?
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3 answers


pred

must be an instance of a type with an overloaded () operator, so it can be called as a function.

struct MyPred
{
    int x;

    bool operator()(int i)
    {
        return (i == x);
    }
};

(Using here struct

for brevity)



std::vector<int> v;

// fill v with ints

MyPred pred;
pred.x = 5;

std::vector<int>::iterator f 
     = std::find_if(v.begin(), 
                    v.end(), 
                    pred);

Writing custom classes like this (with "loads" of code!) Is cumbersome to say the least, but will be greatly improved in C ++ 0x with the addition of lambda syntax.

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You can use equal_to

:



find_if(a.begin(), a.end(), bind2nd(equal_to<int>(), your_value));
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You can use boost :: bind for a more general solution like:

struct Point
{
 int x;
 int y;
};


vector< Point > items;

find_if( items.begin(), items.end(), boost::bind( &Point::x, _1 ) == xValue );

find a point whose x is equal to xValue

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