c++ - 我试图删除文本文件中的一行时留下回车符

Question

在下面的函数中，我创建了一个键，然后在输入文件中搜索它。该函数输出它读取的每一行，除非它与键匹配。

除了在复制最后一条记录后 endl 在文本文件上留下一个回车符外，该函数似乎可以正常工作。当我随后读取文件时，由于返回，它读取了最后一行两次。

我尝试使用空格，结果完全相同。有没有一种方法可以在 while 语句运行后删除最后一个空格或返回？还是我可以避免在最后一条记录上写空格或返回？

void deleteAddress(){
  ifstream infile( "addressbook.txt", ios::in);
  ofstream outfile ("ACopy.txt", ios::out);

  string last, first, address1, address2, address3, address4;
  string address5, address6, bday, anniversary, delL, delF;
  int key, keyDel;

  cout<<"Enter the name of the the client you want to delete (format: last, first)"<<endl;
  cin>> delL >> delF;

  keyDel = createKey(delL,delF);

  while(! infile.eof()) {
    (infile >> last >> first >> address1 >> address2 >> 
               address3 >> address4 >> address5 >> address6 >>
               bday >> anniversary);

    key = createKey(last, first);

    if(key != keyDel) {
      outfile << last << " "<<first << " "<<address1 << " " <<
                 address2 << " "<<address3 << " "<<address4 << 
                 " "<<address5 << " "<<address6 << " "<<bday <<
                 " "<<anniversary<<endl;
    }
  }
  outfile.close();
  infile.close();
}

下面是我正在使用的显示函数(displauCopy)和createKey:

void displayCopy(){
    string line;
    string last, first, address1, address2, address3;
    string address4, address5, address6, bday, anniversary;
    ifstream infile("ACopy.txt");

    cout<<"First" << std::setfill(' ')<<setw(15) << "Last" <<endl;

    while(! infile.eof())
    {
        (infile >> last >> first >> address1 >> address2 >>
                   address3 >> address4 >> address5 >> address6 >>
                   bday >> anniversary);

        cout<< last <<", "<<first<<" "<<address1<<" "
        <<address2<<" "<<address3<<", "<<address4<<", "
        <<address5<<" "<<address6<<" "<<bday<<" "<<anniversary<<endl;
    }
    infile.close();
}

int createKey (string first, string last) {
    int key; 
    key = (int)last[0]+(int)last[1]+(int)last[2]+(int)first[0];
    return key;
} 

Answer 1

问题是你在 EOF-test 上循环，这是个坏主意。

你甚至不检查你的输入是否成功，所以即使它失败了(因为流没有错误，但里面什么都没有)，你仍然会输出一些东西。而且因为这些字符串在循环之外的范围内，所以它们包含最后一次迭代放入其中的任何内容。

您可以进行以下小修改，而不是在 EOF-test 上循环:

while( infile >> last >> first >> address1 >> address2 >> address3
              >> address4 >> address5 >> address6 >> bday >> anniversary )
{
    cout<< last <<", "<<first<<" "<<address1<<" "
        <<address2<<" "<<address3<<", "<<address4<<", "
        <<address5<<" "<<address6<<" "<<bday<<" "<<anniversary<<endl;
}

或者，如果所有内容都在一行中，您可以使用 std::getline 然后从字符串流中读出:

int line_num = 0;
string line;
while( getline( infile, line ) )
{
    ++linenum;
    istringstream iss( line );

    if( iss >> last >> first >> address1 >> address2 >> address3
            >> address4 >> address5 >> address6 >> bday >> anniversary )
    {
        cout<< last <<", "<<first<<" "<<address1<<" "
            <<address2<<" "<<address3<<", "<<address4<<", "
            <<address5<<" "<<address6<<" "<<bday<<" "<<anniversary<<endl;
    }
    else
    {
        cerr << "Error reading line " line_num << " : " << line << endl;
    }
}