c++ - Why does reading a record struct fields from std::istream fail, and how can I fix it?

Question

Suppose we have the following situation:

• A record struct is declared as follows

  struct Person {
      unsigned int id;
      std::string name;
      uint8_t age;
      // ...
  };
  

• Records are stored in a file using the following format:

  ID      Forename Lastname Age
  ------------------------------
  1267867 John     Smith    32
  67545   Jane     Doe      36
  8677453 Gwyneth  Miller   56
  75543   J. Ross  Unusual  23
  ...
  

The file should be read in to collect an arbitrary number of the Person records mentioned above:

std::istream& ifs = std::ifstream("SampleInput.txt");
std::vector<Person> persons;

Person actRecord;
while(ifs >> actRecord.id >> actRecord.name >> actRecord.age) {
    persons.push_back(actRecord);
}

if(!ifs) {
    std::err << "Input format error!" << std::endl;
} 

Question:
What can I do to read in the separate values storing their values into the one actRecord variables' fields?

The above code sample ends up with run time errors:

Runtime error    time: 0 memory: 3476 signal:-1
stderr: Input format error!

Answer 1

One viable solution is to reorder input fields (if this is possible)

ID      Age Forename Lastname
1267867 32  John     Smith    
67545   36  Jane     Doe      
8677453 56  Gwyneth  Miller   
75543   23  J. Ross  Unusual  
...

and read in the records as follows

#include <iostream>
#include <vector>

struct Person {
    unsigned int id;
    std::string name;
    uint8_t age;
    // ...
};

int main() {
    std::istream& ifs = std::cin; // Open file alternatively
    std::vector<Person> persons;

    Person actRecord;
    unsigned int age;
    while(ifs >> actRecord.id >> age && 
          std::getline(ifs, actRecord.name)) {
        actRecord.age = uint8_t(age);
        persons.push_back(actRecord);
    }

    return 0;
}