Reading getline from cin into a stringstream (C++)

问题

So I'm trying to read input like this from the standard input (using cin):

Adam English 85
Charlie Math 76
Erica History 82
Richard Science 90

My goal is to eventually store each data piece in its own cell in a data structure I have created, so basically I want to parse the input so each piece of data is individual. Since each row of input is inputted by the user one at a time, each time I get an entire row of input that I need to parse. Currently I am trying something like this:

stringstream ss;
getline(cin, ss);

string name;
string course;
string grade;
ss >> name >> course >> grade;

The error I am having is that XCode is telling me there's no matching function call to getline which is confusing me. I have included the string library, so I'm guessing the error has to do with using getline to read in from cin to a stringstream? Any help here would be appreciated.

回答1:

You are almost there, the error is most probably¹ caused because you are trying to call getline with second parameter stringstream, just make a slight modification and store the data within the std::cin in a string first and then used it to initialize a stringstream, from which you can extract the input:

// read input
string input;
getline(cin, input);

// initialize string stream
stringstream ss(input);

// extract input
string name;
string course;
string grade;

ss >> name >> course >> grade;

^{1. Assuming you have included:}

#include <iostream>
#include <sstream>
#include <string>

using namespace std;

回答2:

You cannot std::getline() a std::stringstream; only a std::string. Read as a string, then use a stringstream to parse it.

struct Student
{
  string   name;
  string   course;
  unsigned grade;
};

vector <Student> students;
string s;
while (getline( cin, s ))
{
  istringstream ss(s);
  Student student;
  if (ss >> student.name >> student.course >> student.grade)
    students.emplace_back( student );
}

Hope this helps.

回答3:

You can just use cin >> name >> course >> grade; because >> will read until whitespace anyway.

回答4:

Either you don't have a using namespace std in your code or you're not fully qualifying calls made to the API's in the std namespace with an std:: prefix, for example, std::getline(). The solution below parses CSV instead to tokenize values that have whitespace in them. The logic for stdin extraction, parsing the CSV, and converting grade from string to int are all separated. The regex_token_iterator usage is probably the most complicated part, but it uses pretty simple regex for the most part.

// foo.txt:

// Adam,English,85
// Charlie,Math,76
// Erica,History,82
// Richard,Science,90
// John,Foo Science,89

// after compiling to a.exe, run with:
// $ ./a.exe < foo.txt 

// output
// name: Adam, course: English, grade: 85
// name: Charlie, course: Math, grade: 76
// name: Erica, course: History, grade: 82
// name: Richard, course: Science, grade: 90
// name: John, course: Foo Science, grade: 89

#include <iostream>
#include <sstream>
#include <regex>
#include <vector>

using namespace std;

typedef unsigned int uint;

uint stoui(const string &v) {
   uint i;
   stringstream ss;
   ss << v;
   ss >> i;
   return i;
}

string strip(const string &s) {
   regex strip_pat("^\\s*(.*?)\\s*$");
   return regex_replace(s, strip_pat, "$1");
}

vector<string> parse_csv(string &line) {
   vector<string> values;
   regex csv_pat(",");
   regex_token_iterator<string::iterator> end;
   regex_token_iterator<string::iterator> itr(
      line.begin(), line.end(), csv_pat, -1);
   while (itr != end)
      values.push_back(strip(*itr++));
   return values;
}

struct Student {
   string name;
   string course;
   uint grade;
   Student(vector<string> &data) : 
      name(data[0]), course(data[1]), grade(stoui(data[2])) {}
   void dump_info() {
      cout << "name: " << name << 
      ", course: " << course << 
      ", grade: " << grade << endl;
   }
};

int main() {
   string line;
   while (getline(cin, line)) {
      if (!line.empty()) {
         auto csv = parse_csv(line);
         Student s(csv);
         s.dump_info();
      }
   }
}

来源：https://stackoverflow.com/questions/35974402/reading-getline-from-cin-into-a-stringstream-c

标签

c++

cin

getline

stringstream

ostream