Use getline to split a string and check for int

Question

I have a file:

name1 8
name2 27
name3 6

and I'm parsing it into vector. This is my code:

  int i=0;
  vector<Student> stud;

  string line;
  ifstream myfile1(myfile);
  if (!myfile1.is_open()) {return false;}
  else {
    while( getline(myfile1, line) ) {
      istringstream iss(line);
      stud.push_back(Student());
      iss >> stud[i].Name >> stud[i].Grade1;
      i++;
    }
    myfile1.close();
  }

I need to check if the stud[i].Grade1 is int. If it isn't it return false. File can contain:

name1 haha
name2 27
name3 6

How can I do it?

EDIT:

I have tried another way (without getline) and it seems to work. I don't understand why :/

int i=0;
vector<Student> stud;

ifstream myfile1(myfile);
if (!myfile1.is_open()) {return false;}
else {
  stud.push_back(Student());
  while( myfile1 >> stud[i].Name ) {
    if(!(myfile1 >> stud[i].Points1)) return false;
    i++;
    stud.push_back(Student());
}
myfile1.close();
}

http://stackoverflow.com/questions/2844817/how-do-i-check-if-a-c-string-is-an-int — Barış Uşaklı, Mar 14 '13 at 19:56

score 1 · Answer 1 · answered Mar 14 '13 at 20:01

1

If type of Grade1 in numerical such as int, Use std::istringstream::fail() :

// ...
    while( getline(myfile1, line) ) {
      istringstream iss(line);
      stud.push_back(Student());
      iss >> stud[i].Name;
      iss >> stud[i].Grade1;
      if (iss.fail())
        return false;
      i++;
    }
    myfile1.close();
  }
// ...

answered Mar 14 '13 at 20:01

masoud

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I have tried it before, but it always returns false. Even if there are numbers. – user2171413 Mar 14 '13 at 20:03
What's the type of `Grade1` ? – masoud Mar 14 '13 at 20:05
It's int. Code of structure: struct Student { string Name; int Grade1, Grade2; //Student(string name, int grade1, int grade2); }; – user2171413 Mar 14 '13 at 20:06
As you can see, I use `iss >> ...` in two separate statements, I think, it's important. Test my code. – masoud Mar 14 '13 at 20:07
ah, I'm sorry, I didn't see it. It works! Thanks. But what if I have line: name4 27d I forgot to mention that, there must be only number. – user2171413 Mar 14 '13 at 20:10
It has to be in decimal. So just numbers, no letters. – user2171413 Mar 14 '13 at 20:18

score 1 · Answer 2 · edited May 23 '17 at 10:28

It could look like this:

std::vector<Student> students;
std::ifstream myfile1(myfile);
if (!myfile1.is_open())
    return false;

std::string line;
while (std::getline(myfile1, line))
{
    // skip empty lines:
    if (line.empty()) continue;

    Student s;
    std::istringstream iss(line);
    if (!(iss >> s.Name))
        return false;
    if (!(iss >> s.Grade1))
        return false;

    students.push_back(s);
}

just note that iss >> s.Grade1 will succeed not only for decimal, but also for octal and hexadecimal numbers too. To make sure that only decimal value will be read, you could read it into the temporary std::string object and validate it before you use it to retrieve the number. Have a look at How to determine if a string is a number with C++?

Use getline to split a string and check for int

2 Answers2