How to read the given input from text file in C ?-CodePudding

Input:

10.0.0.5 127.0.0.1 3472

10.0.0.11 127.0.0.1 3000

10.0.0.12 127.0.0.1 3030

code:

struct sample{
    string Neighbours;
} input;

int main()
{
string mytext;
 int j=0;
ifstream MyReadFile("/f.txt");
while(getline(MyReadFile,mytext))
{    
  if(j%2==0)
    {
       input.Neighbours=mytext;
    }  
    j  ;
}
cout<<input.Neighbours<<endl;
MyReadFile.close();
}

I am able to get only the last value that is 10.0.0.12 127.0.0.1 3030 as output. what should I do to read all the data and store them into a variable???

CodePudding user response：

The most C way to read a whole file in at once is by using the <iterator> library.

#include <iterator>
#include <string.h>
#include <fstream>
#include <iostream>

int main()
{
    std::ifstream file("input.txt", std::ios::in);

    std::string str ((std::istreambuf_iterator<char>(file)), (std::istreambuf_iterator<char>()));

    std::cout << str << "\n";
}

The output will just be the whole content of "input.txt".

Explanation: In this line

std::string str ((std::istreambuf_iterator<char>(file)), (std::istreambuf_iterator<char>()));

you are using the overloaded std::string constructor to construct a string using a start- and end-iterator. std::istreambuf_iterator<char>(file) returns an iterator to the beginning of file, std::istreambuf_iterator<char>() one to the end by using std::istreambuf_iterator<>()'s default return value.

CodePudding user response：

You only have the last value as output because you are assigning directly to the Neighbours variable input.Neighbours = mytext, you can replace code inside conditional if by this way:

if(j%2==0)
{
    input.Neighbours  = mytext   "\n";
}  
j  ;

The only thing it will do is store them in the variable, but you could also create a vector<string> and then you would have better access to the text extracted from the file.

// print the content of a text file.
#include <iostream>    
#include <fstream>      // std::ifstream
#include <vector>
#include <string>

using namespace std;

struct sample {
    vector<string> Neighbours;
} input;

int main () {
  ifstream file("test.txt");
  string myText;
  int j=0;
  
  while (getline(file, myText)) 
  {
    if (j%2==0) 
      {
        input.Neighbours.push_back(myText);
      }
      j  ;
  }
  
  for (auto &neighbour: input.Neighbours) cout << neighbour << endl;
  return 0;
}

...

10.0.0.5 127.0.0.1 3472
10.0.0.11 127.0.0.1 3000
10.0.0.12 127.0.0.1 3030