Question

我只需要从文本文件中获取特定字符。我在C ++中使用getline()函数。我的编译器一直给我一个错误，即getline()没有匹配的成员函数调用，我该如何解决？我试图从文件中提取姓氏和分数。

文件如下：

Weems 50 60

Dale 51 60

Richards 57 60
...

这是我尝试的代码：

#include <iostream>
#include <cmath>
#include <fstream>

using namespace std;

int main ()
{
    //input variables
    float GradeScore;
    float TotalPoints;
    float GradePercent;
    string LastName;

    ifstream myFile;

    //open file
    myFile.open ("/Users/ravenlawrence/Documents/TestGrades.rtf",ios::in);
    // if file is open
    if (myFile.is_open()) {
        while(!myFile.eof()) {
            string data;
            getline(myFile,data); //reading data on line
            myFile.getline(LastName, ' ');//storing data in LastName 
            myFile.getLine(GradeScore,' ');//storing data in GradeScore 
            myFile.getLine(TotalPoints,' ');//storing data in Total Points 
            cout << LastName << endl;
            // cout<<data<<endl; //print it out
        }
    }
    return 0;
}

Answer 1

从设计开始，将工作分解为小步骤：

open file
loop, reading line from file while more lines
    split line into fields
    convert fields into variables
    display variables

现在解决每一步

// open file
ifstream myFile ("/Users/ravenlawrence/Documents/TestGrades.rtf",ios::in);
if( ! myFile ) {
  cerr << "cannot open file\n";
  exit(1);
}

//loop, reading line from file while more lines
string data;
while( getline( myFile, data ) ) {

   // split line into fields
   std::stringstream sst(data);
   std::string a;
   std::vector<string> vfield;
   while( getline( sst, a, ' ' ) )
       vfield.push_back(a);

   // ignore lines that do not contain exactly three fields
   if( vfield.size() != 3 )
      continue;

   //convert fields into variables
   LastName = vfield[0];
   GradeScore = atof( vfield[1].c_str() );
   TotalPoints = atof( vfield[2].c_str() );

   // display
   ...
}

Answer 2

你不需要在这里使用函数getline，你可以逐字阅读文件。其次，你需要在文件到达eof后关闭它。这是代码：

   int main()
   {
       //input variables
         float GradeScore;
         float TotalPoints;
         float GradePercent;
         string LastName;

         ifstream myFile;

       //open file
         myFile.open("check.txt", ios::in);
      // if file is open
         if (myFile.is_open()) {

           while (!myFile.eof()) {

              myFile >> LastName;//storing data in LastName 
              myFile >> GradeScore;//storing data in GradeScore 
              myFile >> TotalPoints;//storing data in Total Points 

              cout << LastName << endl;
           // cout<<data<<endl; //print it out
           }

         myFile.close();
      }
      system("pause");
      return 0;
      }

不是检查文件是否打开，而是更好的方法是检查文件是否存在：

        if(!myfile)
        {
          cout<<"error!file donot exist";
         }

使用C ++中的getline函数来提取某些字符

2 个答案: