索引的排序向量

Question

I have a very simple question, and I think I am simply doing something stupid, but cannot find the bug for hours....

#include <vector>
#include <algorithm>
#include <iostream>
using namespace std;

typedef unsigned int uint;

enum {ASCEND, DESCEND};

template<typename T>
bool ascend_sort(pair<uint, T> i, pair<uint, T> j){return j.second>i.second;}

template<typename T>
bool descend_sort(pair<uint, T> i, pair<uint, T> j){return i.second>j.second;}

template<typename T>
void sortIdx(vector<uint>& idx, const vector<T>& src, int dir=ASCEND){
    vector< pair<uint, T>  > tmp (src.size());
    for (uint i=0; i<src.size(); i++){
        tmp.push_back(pair<uint, T>(i, src[i]));
        cout << i << " " << src[i] << " \n";
    }

    if (dir==ASCEND){
        sort(tmp.begin(), tmp.end(), ascend_sort<T>);
    }else{
        sort(tmp.begin(), tmp.end(), descend_sort<T>);
    }

    idx.resize(src.size());

    for (uint i=0; i<src.size(); i++){
        idx[i] = (tmp[i].first);
        cout << tmp[i].first << " \n" ;
    }
}

Why does http://ideone.com/HOnvI work and http://ideone.com/R6H0n not....

the codes only differ in sorting ascendantly and descendantly. I also tested sorting without map (sort the vector directly), and it works fine there.

Answer 1

The line

vector< pair<uint, T>  > tmp (src.size());

Creates a vector of size src.size() filled with default elements (here: pair(0, 0.0));

The .push_back() adds additional elements to the end of that array (now the size of (2* src.size() )

Then after the sort you print only the first src.size() elements, which are all the initial 0,0.0 ones

To fix, just declare the vector empty:

vector< pair<uint, T>  > tmp;