Consider the following:

typedef struct {
    int a;
    int b;
    int c;
    int d;
} ABCD;

typedef std::vector<ABCD> VecABCD;

Say I wanted to add up every 'a' member in a vector of type VecABCD. Easy! I just loop through the vector, and sum as I go.

int CalcSumOfA(const VecABCD &vec)
{
    int sumOfA = 0;
    VecABCD::const_iterator it;
    for(it=vec.begin();it!=vec.end();it++)
        sumOfA += it->a;
    return sumOfA;
}

Say I wanted to do the same thing with 'b'? Easy! I'd write....essentially the same function, but with only trivial changes. Same with 'c' and 'd'.

So, is there a more concise, less repetitive way of doing this? I'd like to do something like:

int sumOfA = SumOfMembers(myVec, a);

but I can't conceive of how I'd put such a function together. Ideally, it'd be a template, and I could use it with a vector of any kind of structure, not specifically bound to VecABCD. Anyone have any ideas?

c++ stl
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