C++ how to read what I want from a file? - c++

Question

How can I assign a variable from my C++ code a value from a structured .txt file for example?
If I have this following input.txt structured like this:
<Name> "John Washington"
<Age> "24"
<ID> "19702408447417"
<Alive Status> "Deceased"
In my c++ code if I have
ifstream read("input.txt",ios::in);
char name[64];
read>>name;//name will point to John Washington string
int age;
read>>age;// cout<<age will return 24;
int ID;
read>>ID;// cout<<ID will return 19702408447417
char Alivestatus[32];
read>>Alivestatus;//Alivestatus will point to Deceased string;
How can I make it work like above?

Answer 1

As #πάντα ῥεῖ mentioned in the comments, you will need to implement a parser that can interpret the <> tags within your file. Additionally, I would recommend reconsidering the data types.
Specifically, given that there's no special reason that you're using char [], please switch to std::string. I don't know the use case of your code, but if the input.txt happens to contain data thats larger than the size of the arrays, or even worse if the input is user-controlled, this can easily lead to Buffer Overflows and unwanted exploits. std::string also has the benefit of being standardized, optimized, much more friendly than char arrays, and has a variety of useful algorithms and functions readily available for use.
With regards to text file parsing, you can perhaps implement the following:
#include <fstream>
#include <iostream>
#include <string>
int main()
{
std::ifstream input_file("input.txt");
std::string name_delimeter("<Name> ");
std::string age_delimeter("<Age> ");
std::string id_delimeter("<ID> ");
std::string alive_delimeter("<Alive Status> ");
std::string line;
std::getline(input_file,line);
std::string name(line,line.find(name_delimeter) + name_delimeter.size()); // string for the reasons described above
std::getline(input_file,line);
int age = std::atoi(line.substr(line.find(age_delimeter) + age_delimeter.size()).c_str());
std::getline(input_file,line);
std::string id(line,line.find(id_delimeter) + id_delimeter.size()); // the example ID overflows 32-bit integer
// maybe representing is a string is more appropriate
std::getline(input_file,line);
std::string alive_status(line,line.find(alive_delimeter) + alive_delimeter.size()); // string for the same reason as name
std::cout << "Name = " << name << std::endl << "Age = " << age << std::endl << "ID = " << id << std::endl << "Alive? " << alive_status << std::endl;
}
The basis of the code is just to read the file as it is structured and construct the appropriate data types from them. In fact, because I used std::string for most of the data types, it was easy to build the correct output by means of std::string's constructors and available functions.
Maybe you are performing this in a loop, or the file has several structures. To approach this problem, you can make a Record class that overloads operator >> and reads in the data as required.