Question

我遇到了一个奇怪的问题。我试图用一个函数填充一个向量，然后用另一个函数输出它。即使在调用函数后，向量也显示为空，我相信它正确填充它。到目前为止，这是我的代码。结果是

“输入输入文件名in.txt 在向量中搜索抛出'std :: out_of_range'实例后调用终止 what（）：vector :: _ M_range_check 中止（核心倾倒） “

    #include <iostream>
    #include <cassert>

    #include<vector>
    #include "ArrayUtilities.h"


    using namespace std;

    void fillArray(istream& io, std::vector<int> a, int& actualSize)
    {
       int temp,i=0;
       io>>temp;
       while (temp!=-999)
       {
       a.push_back(temp);
           io>>temp;
           i++;
       }

       actualSize=i;
    }



    void outputArray(ostream& os,
            std::vector<int> a,
            const int actualSize,
            const string& info )
    {
os<<info<<"\n";
for (int w=0;w<actualSize;++w)
{
    os<< a.at(w)<<" ";

}
os<<"\n";
}

int main（） {

int actualSize;
string fileName;
string info;


std::vector<int> a;
cout << "Enter the input file name ";
cin  >> fileName;
ifstream inData;
ofstream outData;
inData.open(fileName.c_str());
outData.open("out.txt");
int searchItem;
inData>>info;
inData>>searchItem;
fillArray  (inData,  a, actualSize);
cout   <<"Search in vector\n";
outData<<"Search in vector\n";
    outputArray(outData, a, actualSize, info);
outputArray(cout,    a, actualSize, info);
//sequential search
int position;
position=seqSearch(a,actualSize,searchItem);
if (position > 0)
    {
        cout    << "Sequential Search: SearchItem "
                << searchItem
                << " is on position "
                << position
                << "\n";
        outData << "Sequential Search: SearchItem "
                << searchItem
                << " is on position "
                << position
                << "\n";
    }
    else
    {
        cout    << "Sequential Search: SearchItem "
                << searchItem
                << " is not in the list\n";
        outData << "Sequential Search: SearchItem "
                << searchItem
                << " is not in the list\n";
    }

感谢您的帮助

Answer 1

您的函数具有向量的本地副本。它不会影响作为参数传递的向量。您可以通过传递对vector：

的引用来解决此问题

void fillArray(istream& io, std::vector<int>& a, int& actualSize)
//                                          ^

Answer 2

juanchopanza在您的代码中显示了错误。我会推荐一种不同的风格。

将fillArray更改为：

std::vector<int> fillArray(istream& io)
{
   std::vector<int> response;
   int temp;
   io>>temp;
   while (temp!=-999) {
       response.push_back(temp);
       io>>temp;
   }
   return response;
}

在main中使用：

int main()
{
    int actualSize;
    string fileName;
    string info;

    std::vector<int> a;
    cout << "Enter the input file name ";
    cin  >> fileName;
    ifstream inData;
    ofstream outData;
    inData.open(fileName.c_str());
    outData.open("out.txt");
    int searchItem;
    inData>>info;
    inData>>searchItem;
    a = fillArray(inData);
    // If you really like actualSize add
    actualSize = a.size();
    cout   <<"Search in vector\n";
    outData<<"Search in vector\n";
        outputArray(outData, a, a.size(), info);
    ...
}

Natuarally我发现它更容易阅读。根据{{3}}的演讲更容易优化。

函数填充矢量但它在某些时候变空。

2 个答案: