How to read multiple lines in c++

Question

I want to read many lines in one go in c++.I know about getline() method but it reads one line completely.Here is something what i want to do.Reading this whole thing in one go

73167176531330624919225119674426574742355349194934
96983520312774506326239578318016984801869478851843
85861560789112949495459501737958331952853208805511
12540698747158523863050715693290963295227443043557
66896648950445244523161731856403098711121722383113
62229893423380308135336276614282806444486645238749
30358907296290491560440772390713810515859307960866
70172427121883998797908792274921901699720888093776
65727333001053367881220235421809751254540594752243
52584907711670556013604839586446706324415722155397
53697817977846174064955149290862569321978468622482
83972241375657056057490261407972968652414535100474
82166370484403199890008895243450658541227588666881
16427171479924442928230863465674813919123162824586
17866458359124566529476545682848912883142607690042
24219022671055626321111109370544217506941658960408
07198403850962455444362981230987879927244284909188
84580156166097919133875499200524063689912560717606
05886116467109405077541002256983155200055935729725
71636269561882670428252483600823257530420752963450

P.S:- when i use getline() method it only reads first line and string length i get is 50 but i want this 1000 character string as whole.Any kind of help?

score 2 · Answer 1 · answered Mar 02 '15 at 08:34

2

If you know the number of characters in each line, and you how many lines you want to read, you can just use fread or istream::read to read a specific number of characters.

Keep in mind the line endings though.

answered Mar 02 '15 at 08:34

Tafuri

468
2
7

ok i agree,it will be good for this question.But i was asking as general case – sneha sharma Mar 02 '15 at 08:35
2

What is the general case then, if you want to read the complete file into a string you can just use the method described in this answer: http://stackoverflow.com/a/2602060/1784021 – Tafuri Mar 02 '15 at 08:38
general case means if i dont know no. of characters in each line – sneha sharma Mar 02 '15 at 08:39
1

The answer i linked above will solve that for you. To read a specific number of lines, of unknown length, and get them all in one string. Just use `getline()` and append each line to your final string. – Tafuri Mar 02 '15 at 08:45

score 1 · Answer 2 · answered Mar 02 '15 at 08:42

1

Get the size of the file N using ifstream methods.

myfile.seekg (0, ios::end);
int N = myfile.tellg();

Read N bytes.

answered Mar 02 '15 at 08:42

James Bear

309
1
3

score 0 · Answer 3 · answered Mar 24 '15 at 16:59

Use read(buffer,size) when you want to read those 1000 characters string in one go.

#include <iostream.h>
#include <fstream.h>
#include <stdlib.h>
#include <string.h>
int main () 
{

       char buffer[1000];
       long size;

       ifstream infile ("numbers.txt",ifstream::binary);

       // get size of file
       infile.seekg(0,ifstream::end);
       size=infile.tellg();
       infile.seekg(0);

       //reset buffer to ' '
       memset(buffer,32,sizeof(buffer ));

       // read file content into buffer
       infile.read (buffer,size);

       // display buffer
        cout<<buffer<<"\n\n";

       infile.close();    



  cout<<" \nPress any key to continue\n";
  cin.ignore();
  cin.get();


  return 0;
}

Output:

73167176531330624919225119674426574742355349194934
96983520312774506326239578318016984801869478851843
85861560789112949495459501737958331952853208805511
12540698747158523863050715693290963295227443043557
66896648950445244523161731856403098711121722383113
62229893423380308135336276614282806444486645238749
30358907296290491560440772390713810515859307960866
70172427121883998797908792274921901699720888093776
65727333001053367881220235421809751254540594752243
52584907711670556013604839586446706324415722155397
53697817977846174064955149290862569321978468622482
83972241375657056057490261407972968652414535100474
82166370484403199890008895243450658541227588666881
16427171479924442928230863465674813919123162824586
17866458359124566529476545682848912883142607690042
24219022671055626321111109370544217506941658960408
07198403850962455444362981230987879927244284909188
84580156166097919133875499200524063689912560717606
05886116467109405077541002256983155200055935729725
71636269561882670428252483600823257530420752963450


Press any key to continue

How to read multiple lines in c++

3 Answers3