std::map with struct as key

Question

i'm try to use a std::map with the key as Struct, but it fails on find the key. what is wrong here? Find does not find but insert will not change the count in the map.....

#pragma once
#include <map>
struct OccTestdef
{

public:
    int Typ;
    int Length;

    OccTestdef(int typ,  int length) :Typ(typ), Length(length) {};

    bool operator < (const OccTestdef& R) const
    {
        if (Typ < R.Typ)  return true;
        if (Length < R.Length) return true;
        return false;
    }

};


typedef std::map<OccTestdef, int> Testmap;
typedef std::pair<OccTestdef, int> Testpair;

class testocc
{
public:
    testocc();
    ~testocc(){}

    bool runtest();

private:
    Testmap tests;

    int addOrInsert(int left, int num, int value);

};

and the cpp:

#include "testocc.h"

testocc::testocc()
{
    tests = Testmap();
}

// Will Return the Map-Value if found or -1 if new Inserted
int testocc::addOrInsert(int left, int num, int value)
{
    int res;
    OccTestdef tn(left, num);
    auto result = tests.find(tn);
    if (result != tests.end()) {
        res = result->second;
    }
    else
    {
        tests.insert(Testpair(tn, value));
        res = -1;
    }
    return res;
}

bool testocc::runtest()
{
    int res;
    bool result;
// Fill map with 4 Entries
    tests.insert(Testpair( OccTestdef(1, 100), 1));
    tests.insert(Testpair(OccTestdef(1, 200), 2));
    tests.insert(Testpair(OccTestdef(1, 300), 3));
    tests.insert(Testpair(OccTestdef(1, 400), 4));


    result = (tests.size() == 4);
// Try to find or Insert 
     res = addOrInsert(1, 200, 2);
    //res should be 2 
    result = (res == 2);

    result = (tests.size() == 4);

    res = addOrInsert(2, 200, 20);
    // Res must be -1 because new inserted
    result = (res == -1);

    // Count is not changed
    result = (tests.size() == 5);


//These fails why?
    res = addOrInsert(2, 200, 20);
    //res should be 20 
    result = (res == 20);
    return result;
}

I don't understand why the test.find() is not working as expected.

More specifically, your operator< is not a Strict Weak Ordering because given OccTestdef a(1,2); OccTestdef b(2,1); you have both a < b and b < a returning true. — aschepler
– aschepler, Commented Jun 24, 2017 at 13:22

GWW · Accepted Answer · 2017-06-24 13:20:43Z

1

Your opeator< will not order your elements properly because you return true if Typ is smaller or if Length is smaller.

#include <tuple>

bool operator < (const OccTestdef& R) const
{
    return std::tie(Typ, Length) < std::tie(R.Typ, R.Length);
}

answered Jun 24, 2017 at 13:20

GWW

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1 Comment

Fritzw Over a year ago

Thanks, i think sometimes i need a break

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