Question

我遇到的问题是我需要使用copy函数从union_set函数打印结果集。（所以我不允许将输出作为set_union函数的最后一项）。我似乎无法让copy函数正确地为lastAunionB指针工作（我还需要几次）。我目前所拥有的只是我最后一次尝试答案，尽管我尝试了更多的东西。我对复制功能做错了什么？这是代码。

#include <iostream>
#include <iterator>
#include <set>
#include <algorithm>
#include <vector>

using namespace std;

int main()
{
    int setA[5] = {2, 4, 5, 7, 8};
    int setB[7] = {1, 2, 3, 4, 5, 6, 7};
    int setC[5] = {2, 5, 8, 8, 15};
    int setD[6] = {1, 4, 4, 6, 7, 12};

    set<int> set2A(setA,setA+5);
    set<int> set2B(setB,setB+7);
    set<int> set2C(setC,setC+5);
    set<int> set2D(setD,setD+6);


    int AunionB[12];
    int AunionC[10];
    int BunionD[13];
    int AintersectB[12];
    int AintersectC[10];

    set<int> finalUnion;
    set<int> finalIntersection;
    set<int> final2Union;
    set<int> final2Intersection;
    set<int> final2Difference;
    ostream_iterator< int > output( cout, " " );

    int *lastAunionB;
    int *lastAunionC;
    int *lastBunionD;
    int *lastAintersectB;
    int *lastAintersectC;

    cout << "setA = ";
    copy(set2A.begin(), set2A.end(), output);
    cout << endl;

    cout << "setB = ";
    copy(set2B.begin(), set2B.end(), output);
    cout << endl;

    cout << "setC = ";
    copy(set2C.begin(), set2C.end(), output);
    cout << endl;

    cout << "setD = ";
    copy(set2D.begin(), set2D.end(), output);
    cout << endl;

    //here is where the problem lies
    cout << "AunionB = ";
    lastAunionB = set_union(setA, setA+5, setB, setB+7, AunionB);
    copy(lastAunionB, lastAunionB, output);
    cout << endl;

    /*
    cout << "AunionC = ";
    set_union(setA, setA+5, setC, setC+5, AunionC);
    cout << endl;

    cout << "BunionD = ";
    set_union(setB, setB+7, setD, setD+6, BunionD);
    cout << endl;

    cout << "AintercectB = ";
    set_intersection(setA, setA+5, setB, setB+7, AintersectB);
    cout << endl;

    cout << "AintercectC = ";
    set_intersection(setA, setA+5, setC, setC+7, AintersectC);
    cout << endl;

    */

    return 0;

}

Answer 1

lastAunionB = set_union(setA, setA+5, setB, setB+7, AunionB);
copy(lastAunionB, lastAunionB, output);

传递给set_union的最后一个参数将对应于构建的新集合范围的开头。 set_union的返回值将是此范围的结尾。

你想要lastAunionB和其他原始指针以及你作为迭代器传递的几乎所有内容都是用类型std::set<int>::iterator定义的，并且你想要复制范围像这样：

std::copy(AunionB, lastAunionB, output);

Answer 2

您正试图从空范围内复制。

copy(ptr,ptr,output);

永远不会打印任何内容。

使用复印功能进行打印设置

2 个答案: