c++ - 为什么从 std::istream 读取记录结构字段失败，我该如何解决？

Question

假设我们有以下情况:

• 记录结构声明如下

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

• 记录使用以下格式存储在文件中:

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

应该读入文件以收集任意数量的上述Person记录:

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;
} 

问题:
我可以做些什么来读取单独的值，将它们的值存储到一个 actRecord 变量的字段中？

以上code sample以运行时错误结束:

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

Answer 1

一个viable solution是重新排序输入字段(如果可能的话)

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

读入记录如下

#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;
}