读出一个大txt文件 [英] readout a big txt file

问题描述

我想知道，如果有另一种方式读出大文件

  Hans // name 
 
 Bachelor // study_path 
 
 WS10_11 //学期
 
 22 //年龄
  

而不是这样：

  fout>名称; // string 
 
 fout>> study_path; // string 
 
 fout>>学期; // string 
 
 fout>>年龄;当我的文件变成20多行时，我应该使20多个fouts？/ / int 
  

有另一种方法吗？

解决方案

每个人的数据：

  class Person {
 public：
 std :: string name; 
 std :: string study_path; 
 std :: string semester; 
 unsigned int age; 
}; 
  

然后您可以为该类定义流提取运算符：

  std :: istream& operator>>（std :: istream& stream，Person& person）{
 stream>> person.name>> person.study_path>> person.semester>>人士; 
 return stream; 
} 
  

然后你可以读取整个文件：

  std :: ifstream file（datafile.txt）; 
 std :: vector< Person>数据; 
 std :: copy（std :: istream_iterator< Person>（file），std :: istream_iterator< Person>（），
 std :: back_inserter 
  

这将读取整个文件，并将所有提取的记录存储在 。如果您知道您将提前读取的记录数，可以在读取文件之前调用 data.reserve（number_of_records）。因此，向量将具有足够的存储器来存储所有记录而不重新分配，如果文件较大，则可能加速加载。

i want to know, if there is another way to readout a big file

Hans //name

Bachelor // study_path

WS10_11 //semester

22 // age 

and not like this:

fout >> name; //string

fout >> study_path; //string

fout >> Semester ; //string

fout >> age; //int

when my file turns to more than 20 line's i should make 20+ fouts?

Is there another way?

解决方案

You could define a class to hold the data for each person:

class Person {
public:
    std::string name;
    std::string study_path;
    std::string semester;
    unsigned int age;
};

Then you can define a stream extraction operator for that class:

std::istream & operator>>(std::istream & stream, Person & person) {
    stream >> person.name >> person.study_path >> person.semester >> person.age;
    return stream;
}

And then you can just read the entire file like that:

std::ifstream file("datafile.txt");
std::vector<Person> data;
std::copy(std::istream_iterator<Person>(file), std::istream_iterator<Person>(),
          std::back_inserter(data));

This will read the entire file and store all the extracted records in a vector. If you know the number of records you will read in advance, you can call data.reserve(number_of_records) before reading the file. Thus, the vector will have enough memory to store all records without reallocation, which might potentially speed up the loading if the file is large.

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