c++ how to copy specific lines from a file to another?

Question

I want to write a program that will copy a few lines in a file in another file. for example copy line 5 to 100 from file a and write it to file b. thanks

this is my code.but my code copying all content of file a to file b.

#include <iostream>
#include <fstream>
using namespace std;

int main(){
   char line[100];

   ifstream is("a.txt");
   ofstream os("b.txt");

   if (is.is_open()){
      while (!is.eof()){
         is.getline(line,100,'\n');
         os << line << endl;
         }
   }
   else{
      cout << "a.txt couldn't be opened. Creat and write something in a.txt, and try again." << endl;
   }

   return 0;
}

You need to count the lines as you read them so you know when to copy. — Galik, Oct 03 '14 at 01:46
OT: See http://stackoverflow.com/questions/5431941/while-feof-file-is-always-wrong — Barmar, Oct 03 '14 at 01:58

Jay · Answer 1 · 2014-10-03T16:37:24.733

2

Here is another way to do it:

 std::ofstream outFile("/path/to/outfile.txt");
 std::string line;

 std::ifstream inFile("/path/to/infile.txt");
 int count = 0;
 while(getline(inFile, line)){

     if(count > 5 && count < 100){
        outFile << line << std::endl;
     }
     count++;
 }
 outFile.close();
 inFile.close();

edited Oct 03 '14 at 16:37

answered Oct 03 '14 at 01:57

Jay

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hi.Thanks for your response.but b file stored empty.it seems this code just create an empty file b. – alibag90 Oct 03 '14 at 13:00
Sorry I missed the `count++` in the while loop – Jay Oct 03 '14 at 16:37
Closing the streams is not necessary. RAII will take care of it. – Leśny Rumcajs Jan 19 '19 at 10:39

c++ how to copy specific lines from a file to another?

1 Answers1