C++：将 ifstream 与 getline() 结合使用；

Question

Check this program

ifstream filein("Hey.txt");
filein.getline(line,99);
cout<<line<<endl;
filein.getline(line,99);
cout<<line<<endl;
filein.close();

The file Hey.txt has alot of characters in it. Well over a 1000

But my question is Why in the second time i try to print line. It doesnt get print?

Answer 1

The idiomatic way to read lines from a stream is this:

std::ifstream filein("Hey.txt");

for (std::string line; std::getline(filein, line); ) 
{
    std::cout << line << std::endl;
}

Notes:

• No close() . C++ takes care of resource management for you when used idiomatically.

• Use the free std::getline , not the stream member function.

Answer 2

According to the C++ reference ( here ) getline sets the ios::fail when count-1 characters have been extracted. You would have to call filein.clear(); in between the getline() calls.

Answer 3

#include<iostream>
using namespace std;
int main() 
{
ifstream in;
string lastLine1;
string lastLine2;
in.open("input.txt");
while(in.good()){
    getline(in,lastLine1);
    getline(in,lastLine2);
}
in.close();
if(lastLine2=="")
    cout<<lastLine1<<endl;
else
    cout<<lastLine2<<endl;
return 0;
}

Answer 4

正如 Kerrek SB 所说，有两种可能性：1）第二行是空行 2）没有第二行，所有超过 1000 个字符都在一行中，所以第二个getline没有什么可获取的。

Answer 5

An easier way to get a line is to use the extractor operator of ifstream

    string result;
    //line counter
    int line=1;
    ifstream filein("Hey.txt");
    while(filein >> result)
    { 
      //display the line number and the result string of reading the line
      cout << line << result << endl;
      ++line;
    }

One problem here though is that it won't work when the line have a space ' ' because it is considered a field delimiter in ifstream . If you want to implement this kind of solution change your field delimiter to eg - / or any other field delimiter you like.

If you know how many spaces there is you can eat all the spaces by using other variables in the extractor operator of ifstream. Consider the file has contents of first name last name.

    //file content is: FirstName LastName
    int line=1;
    ifstream filein("Hey.txt");
    string firstName;
    string lastName;
    while(filein>>firstName>>lastName)
    {
      cout << line << firstName << lastName << endl;
    }