docs/CPC/CpcCppExample.md

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# CPC Sketch C++ Example

    #include <iostream>
    #include <fstream>
    
    #include <cpc_sketch.hpp>
    #include <cpc_union.hpp>
    
    //simplified file operations and no error handling for clarity
    int main(int argc, char **argv) {
      const int lg_k = 10;
    
      // this section generates two sketches with some overlap and serializes them into files
      {
        // 100000 distinct keys
        datasketches::cpc_sketch sketch1(lg_k);
        for (int key = 0; key < 100000; key++) sketch1.update(key);
        std::ofstream os1("cpc_sketch1.bin");
        sketch1.serialize(os1);
    
        // 100000 distinct keys
        datasketches::cpc_sketch sketch2(lg_k);
        for (int key = 50000; key < 150000; key++) sketch2.update(key);
        std::ofstream os2("cpc_sketch2.bin");
        sketch2.serialize(os2);
      }
    
      // this section deserializes the sketches, produces union and prints the result
      {
        std::ifstream is1("cpc_sketch1.bin");
        auto sketch1 = datasketches::cpc_sketch::deserialize(is1);
    
        std::ifstream is2("cpc_sketch2.bin");
        auto sketch2 = datasketches::cpc_sketch::deserialize(is2);
    
        datasketches::cpc_union u(lg_k);
        u.update(sketch1);
        u.update(sketch2);
        auto sketch = u.get_result();
    
        // debug summary of the union result sketch
        sketch.to_string();

        std::cout << "Distinct count estimate: " << sketch.get_estimate() << std::endl;
        std::cout << "Distinct count lower bound 95% confidence: " << sketch.get_lower_bound(2) << std::endl;
        std::cout << "Distinct count upper bound 95% confidence: " << sketch.get_upper_bound(2) << std::endl;
      }
    
      return 0;
    }

    Output:
    ### CPC sketch summary:
       lg_k           : 10
       seed hash      : 93cc
       C              : 7706
       flavor         : 4
       merged         : true
       intresting col : 4
       table entries  : 27
       window         : allocated
       window offset  : 5
    ### End sketch summary
    Distinct count estimate: 149797
    Distinct count lower bound 95% confidence: 143416
    Distinct count upper bound 95% confidence: 156397