Question

在下面的C ++代码中，我想使用模板函数来确定两个向量是否完全相同，但是，我总是从模板函数中得到错误。你能给我一些关于如何从模板函数返回布尔值的建议吗？（我的C ++编译器是g ++ 4.6）

编辑：在pop_back p1 p2 p3 p4之后，结果现在与我的预期相匹配。

#include <iostream>
#include <memory>
#include <vector>

using namespace std;

template<class T> bool areTheyMatched(shared_ptr<vector<T>> p1, shared_ptr<vector<T>> p2) {
if ((*p1).size() == (*p2).size()) {
    cout << (*p1).size() << endl;
    for (unsigned int i = 0;  i < (*p1).size(); i++) {
      if ((*p1)[i] != (*p2)[i]) {
        cout << (*p1)[i] << " " <<  (*p2)[i] << endl;   
        return false;
          } 
        }
 } else {
    return false;
 }
 cout << "All elements are exactly the same" << endl;
 return true;
 }


 int main(int argc, char *argv[]) {
   shared_ptr<vector<int>> p1(new vector<int>);
   shared_ptr<vector<int>> p2(new vector<int>);
   shared_ptr<vector<double>> p3(new vector<double>);
   shared_ptr<vector<double>> p4(new vector<double>);
   for (int i = 0; i < 10; i++) 
     (*p1).push_back(i); 
   for (int i = 0; i < 9; i++) 
     (*p2).push_back(i);
   (*p2).push_back(11);
   for (double i = 0.0; i < 9.9; i += 1.1) 
      (*p3).push_back(i);
   for (double i = 0.0; i < 8.8; i += 1.1) 
      (*p4).push_back(i);
   (*p4).push_back(11.0);
   cout << "Case 1: " << areTheyMatched(p1, p2) << endl;
   (*p1).pop_back();
   (*p2).pop_back();
   cout << "Case 2: " << areTheyMatched(p1, p2) << endl;
   cout << "Case 3: " << areTheyMatched(p3, p4) << endl;
   (*p3).pop_back();
   (*p4).pop_back();
   cout << "Case 4: " << areTheyMatched(p3, p4) << endl;
   p1.reset();
   p2.reset();
   p3.reset();
   p4.reset();
   return 0;
}

Answer 1

模板代码看起来很好，但测试向量从不相同，是不是。

首先，他们中的一个具有元素11，并且当移除它们时它们具有不同的尺寸。

Answer 2

你的矢量真的与众不同。

   for (int i = 0; i < 10; i++) 
     (*p1).push_back(i); 
   for (int i = 0; i < 9; i++) 
     (*p2).push_back(i);
   (*p2).push_back(11);

p1 = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
p2 = {0, 1, 2, 3, 4, 5, 6, 7, 8, 11}
Case 1: false
(*p2).pop_back();
p1 = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
p2 = {0, 1, 2, 3, 4, 5, 6, 7, 8}
Case 2: false

Answer 3

你的模板功能完全正常......

你得到错误的原因是因为你的输入真的不同，最初是在内容上，并且在弹出后甚至大小都不匹配。

你有没有理由使用shared_ptr？你可以传递矢量＆amp;除非你有充分理由需要共享指针，否则你不应该使用它们。虽然当您需要跨多个实体共享数据时，它们是传递指针的最佳方式，但它们会产生开销。

Answer 4

如果您检测代码，您将看到它正常工作。我需要使用std::tr1和<tr1/memory>以及> >代替>>来使用G ++ 4.6.1进行编译，但这显示了它的工作原理：

#include <iostream>
#include <tr1/memory>
#include <vector>

using namespace std;
using namespace std::tr1;

template<class T> bool areTheyMatched(shared_ptr< vector<T> > p1, shared_ptr< vector<T> > p2)
{
    cout << "p1.size: " << (*p1).size() << ", p2.size: " << (*p2).size() << endl;
    if ((*p1).size() != (*p2).size())
        return false;
    for (unsigned int i = 0;  i < (*p1).size(); i++)
    {
        if ((*p1)[i] != (*p2)[i])
        {
            cout << "i = " << i << ": " << (*p1)[i] << " " <<  (*p2)[i] << endl;   
            return false;
        }
    }
    cout << "All elements are exactly the same" << endl;
    return true;
}

int main()
{
   shared_ptr< vector<int> > p1(new vector<int>);
   shared_ptr< vector<int> > p2(new vector<int>);
   shared_ptr< vector<double> > p3(new vector<double>);
   shared_ptr< vector<double> > p4(new vector<double>);
   for (int i = 0; i < 10; i++) 
     (*p1).push_back(i); 
   for (int i = 0; i < 9; i++) 
     (*p2).push_back(i);
   (*p2).push_back(11);
   for (double i = 0.0; i < 9.9; i += 1.1) 
      (*p3).push_back(i);
   for (double i = 0.0; i < 8.8; i += 1.1) 
      (*p4).push_back(i);
   (*p4).push_back(11.0);

   cout << "Case 1: " << areTheyMatched(p1, p2) << endl;
   (*p2).pop_back();
   cout << "Case 2: " << areTheyMatched(p1, p2) << endl;
   (*p1).pop_back();
   cout << "Case 2a: " << areTheyMatched(p1, p2) << endl;

   cout << "Case 3: " << areTheyMatched(p3, p4) << endl;
   (*p3).pop_back();
   cout << "Case 4: " << areTheyMatched(p3, p4) << endl;
   (*p4).pop_back();
   cout << "Case 4a: " << areTheyMatched(p3, p4) << endl;
   p1.reset();
   p2.reset();
   p3.reset();
   p4.reset();
   return 0;
}

输出

p1.size: 10, p2.size: 10
i = 9: 9 11
Case 1: 0
p1.size: 10, p2.size: 9
Case 2: 0
p1.size: 9, p2.size: 9
All elements are exactly the same
Case 2a: 1
p1.size: 10, p2.size: 10
i = 9: 9.9 11
Case 3: 0
p1.size: 9, p2.size: 10
Case 4: 0
p1.size: 9, p2.size: 9
All elements are exactly the same
Case 4a: 1

如何从模板函数返回布尔值？

4 个答案:

输出