Changing information in a specific spot in a file

[stor3159]

I have a text file, let's call it "words.txt"

words.txt reads exactly as follows:

line1 word1 word2 word3
line2 word1 word2 word3
line3 word1 word2 word3

I have a function that initializes a line depending on user input so that they are as follows:

string var1, var2, var3, var4;
var1 = line[cin];
var2 = word1;
var3 = word2;
var4 = word3;
//not the code, just the result of initializer 

Say I wanted to change word2 on line2 to whatever the user inputs there, say "baloney":

line1 word1 word2 word3
line2 word1 baloney word3
line3 word1 word2 word3

What's the best way of going about that?

[salem c]

Excluding the very special case where changes result in no change to the length (or encoding) of a word, you basically have to
- read in each line in turn.
- decide if you need to change the line in some way.
- write out the (possibly modified) line to a new temporary file.

When you're done, you can then decide to
- rename the original file to say 'file.bak', then rename the temporary to file.txt
- Forego the backup, and just replace file.txt with the newly created temporary.

[lastchance]

#include <iostream>
#include <fstream>
#include <sstream>
#include <vector>
#include <string>
using namespace std;


template<typename M> void printIt( const M matrix )
{
   for ( auto &row : matrix )
   {
      for ( auto e : row ) cout << e << " ";
      cout << '\n';
   }
}


int main()
{
   string line, word;
   vector< vector<string> > page;
   ifstream in( "words.txt" );
   while( getline( in, line ) )
   {
      stringstream ss( line );
      vector<string> vline;
      while ( ss >> word ) vline.push_back( word );
      page.push_back( vline );
   }

   cout << "Before:\n";
   printIt( page );

   int row = 2, col = 2;
   page[row-1][col-1] = "Brexit";

   cout << "\nAfter:\n";
   printIt( page );
}

Before:
word1 word2 word3 
word1 word2 word3 
word1 word2 word3 

After:
word1 word2 word3 
word1 Brexit word3 
word1 word2 word3