How to search record using an id

I am creating the system that outputs all the registered student in one of my textfile e.g

123 Michael
412 Voker
512 Karl
143 Riki

I need to use their ID to search for the student Means i need to read this register student file.

The system will only ask for the ID. e.g

Type ID num: 123

OUTPUT:

Hello Michael your ID number is 123.

回答1:

Probably your are looking for a struct or class. Make a Student class I would say.

class Student{
     public:
         int id;
         char *name;
};

Student s;

Give a go through the link [1] to understand how you can read or write a Student object from or to a file respectively.

[1] https://www.geeksforgeeks.org/readwrite-class-objects-fromto-file-c/

回答2:

Hang on, here I have compiled a working example covering all your posted questions.

The below solution though is written in a very idiomatic c++ way (the solution sports a usage of stream_iterators when writing/reading files for a non-trivial container data type (i.e. std::map):

#include <iostream>
#include <map>
#include <sstream>
#include <algorithm>    // copy, ...
#include <utility>      // pair, ...    
#include <fstream>
#include <iterator>
using namespace std;


typedef map<size_t, string> directory;
typedef pair<size_t, string> dir_kv_pair;

struct kv_dir : public dir_kv_pair {
                        kv_dir(void) = default;
                        kv_dir(directory::value_type kv):       // type conversion helper
                         dir_kv_pair{kv} {}                     // pair <-> kv_dir
    friend ostream &    operator<<(ostream & os, const kv_dir &kv)
                         { return os << kv.first << " " << kv.second << endl; }
    friend istream &    operator>>(istream & is, kv_dir& kv) {
                         if((is >> kv.second).eof()) return is;
                         kv.first = stol(kv.second);
                         return is >> kv.second;
                        }
};


int main()
{ 
 string fname = "dir.txt";

 {  // write into file
  directory dir;

  // filling the container
  dir[123] = "Michael";
  dir[412] = "Voker";
  dir[512] = "Karl";
  dir[143] = "Riki";

  // writing to file:
  ofstream fout{fname};
  copy(dir.begin(), dir.end(), ostream_iterator<kv_dir> {fout});
 }

 // reading from file:
 directory dir{ istream_iterator<kv_dir>{ ifstream{fname} >> skipws }, 
                istream_iterator<kv_dir>{} };

 // finding by ID
 size_t id = 512;
 cout << "Pupil id [" << id << "]: " << (dir.count(id) == 1? dir[id]: "not found") << endl;
}

Sample output:

Pupil id [512]: Karl
bash $
bash $ cat dir.txt 
123 Michael
143 Riki
412 Voker
512 Karl
bash $