while循环应测试ifstream是否为eof或使用good（）时出错。 getline只返回文件流而不是布尔表达式。

The while loop should test if the ifstream is at eof or an error using good(). getline only returns the file stream not a boolean expression.

int main()
{
string _search;
string line;
ifstream read;

int i =0;
    while(i++<2)
    {
        cout<<"Enter the word to search"<<endl;
        cin>>_search;
        read.open("type.txt");
        size_t pos,i=0;
        if(read.is_open())
        {
            while (read.good())
            {
                i++;
                getline(read,line);
                pos = line.find(_search);
                if(pos != string::npos)
                {
                   cout<<i<<": "<<line<<endl;
                }
                else
                {
                    cout<<"Not found"<<endl;
                }

            }
            read.close();
        }

    }
}

#include <iostream>
#include <fstream>
#include <string>

using namespace std;
 

int main()
{
 
  string search,line;
  ifstream read;
 
  int i =0;
 
  while(i<2)
  {
    read.open("type.txt");
 
  cout<<"Enter the word to search"<<endl;
  cin>>search;
 
  size_t pos;
  if(read.is_open())
  {
	  while (getline(read,line))
	  {
		   pos = line.find(search);
			   if(pos != string::npos)
			  {
				  
 
				  cout<<line<<endl;
				  
				  read.close();
 
			   }
	  }
 
	  
 

 

	  }
 
  i++;
 

 
  }
 

 

 

 
  system("pause");
 

 

 

 
  }