creating an large array of objects c++

Question

I need to create a large array(1000) of histograms where each histogram is slightly different. I am new to C++ and my first thought on how to do this was using a for loop which will create the histogram and add it to the array in the loop, but ive run into the issue of variable names (which i expected). How can i make the variable name of each histogram different while adding them in the loop?

sorry if that was poorly worded.

C++ has built-in arrays; only one name needed. Better yet, use std::vector. — Qaz
– Qaz, Commented Jun 15, 2012 at 19:46
We can help you better if you show us the relevant parts of your code ;) — Hans Z
– Hans Z, Commented Jun 15, 2012 at 19:47
Welcome to SO. Try to include code, even if it's clunky or not working, otherwise it's hard to understand your point of view. Also, you can use Histogram myHistograms[1000] or std::vector<Histrogram> myHistograms. But the actual implementation depends on your Histogram, especially its constructor and assignment methods. — Zeta
– Zeta, Commented Jun 15, 2012 at 19:51
You may have to use dynamic memory as most compilers have smaller limit for static memory allocations. — Thomas Matthews
– Thomas Matthews, Commented Jun 15, 2012 at 20:16

jxh · Accepted Answer · 2012-06-16 14:12:45Z

4

It sounds like what you want is a histogram class where each instance is a little different.

class Histogram {
    unsigned m_count;
    std::string m_label;
public:
    Histogram(std::string label) : m_count(0), m_label(label) {}
    std::string & label () { return m_label; }
    std::string label () const { return m_label; }
    unsigned & count () { return m_count; }
    unsigned count () const { return m_count; }
};

It might be easier to manage these within a map rather than a vector (unless you can actually classify the input into a number), but each histogram will need a unique label.

std::map<std::string, std::unique_ptr<Histogram> > histograms;

while (more_input()) {
    input = get_input();
    std::string classification = classify_input(input);
    if (histograms[classification] == 0)
        histograms[classification]
            = std::unique_ptr<Histogram>(new Histogram(classification));
    histograms[classification]->count() += 1;
}

edited Jun 16, 2012 at 14:12

answered Jun 15, 2012 at 19:59

jxh

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1 Comment

Xavier Hubbard Anderson Over a year ago

as it turns out i am an idiot and i was doing the wrong thing all along. Thank you all so much for your help though.

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