Go Premium for a chance to win a PS4. Enter to Win

x
?
Solved

How do I write/read to/from a specific line of a txt(or ini) file in C++?

Posted on 2008-06-26
4
Medium Priority
?
380 Views
Last Modified: 2013-11-17
How do I write/read to/from a specific line of a txt(or ini) file in C++? e.g I want to write this string "abc" in the line 13 of text file c:\text.txt , or return label1's caption the string in line 14 of c:\text.txt .
thanks
0
Comment
Question by:Chrysaor
4 Comments
 
LVL 53

Assisted Solution

by:Infinity08
Infinity08 earned 200 total points
ID: 21876912
Take a look at this good tutorial on file I/O in C++ :

        http://www.cplusplus.com/doc/tutorial/files.html
0
 
LVL 12

Accepted Solution

by:
trinitrotoluene earned 300 total points
ID: 21877887
inserting is not usually possible, but you can try overwriting existing content. Check my sample code for this.

A better way would be read the file content to a buffer and then modify the contents of the buffer and then write it back to the file. You can try this exercise.
#include <iostream>
#include <fstream>
 
using namespace std;
 
 
main()
{
 ifstream fin("c:\\text.txt", ios::in);
 
 
  string s;
  int linecnt = 0;
 
 while(getline(fin, s))
 {
   linecnt++;
   cout<<s<<endl;    
   if (linecnt==13)
   {
     long changepos = fin.tellg();     
     cout<<changepos;
     
     fin.close();
     ofstream fop("c:\\text.txt", ios::ate|ios::out|ios::in);      
        
          
     fop.seekp(changepos);
     fop<<"abc";
     fop.close();
   }
   
 } 
 
}

Open in new window

0
 
LVL 25

Assisted Solution

by:kode99
kode99 earned 300 total points
ID: 21879316
CBuilder actually makes this really really simple.  By using a TStringList class  you can load a text file into a array of strings which then lets you edit as you wish then save.  This is the same method a TMemo component uses for the text it contains.

So to set one line to 'abc' and read back a caption title would be as follows:

TStringList *sList = new TStringList();
sList->LoadFromFile("text.txt");

sList->Strings[12] = "abc";   // note that the index starts with line 1 at 0

Label1->Caption = sList->String[13];

sList->SaveToFile("text.txt");

Of course you would want to check and make sure there are 12 or 13 lines before trying to access them.  Check out the help file on TStringList for more examples.

Further if you want to use .ini files there is also a TIniFile class that will take care of the formatting.  So the file will use the keyname = value format along with sections.  The help file contains a good example of its use.  There is also a class for using the registry instead of ini files.

0
 
LVL 46

Assisted Solution

by:Kent Olsen
Kent Olsen earned 200 total points
ID: 21880380
Hi Chrysaor,

Though there are a lot of similarities, there are many differences in writing a random line in a text file and a random line in an configuration file.  In both cases, you must rewrite the file past the location that you change.

If you're writing a configuration file, there may be a very good "easy way" for you.  The TIniFile class manages configuration files and lets you easily change specific values or add/delete values (lines).  The class will do all of the work of rewriting the file for you.

Check out the help on the TIniFile.  It's worth knowing.

Kent
0

Featured Post

Technology Partners: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Templates For Beginners Or How To Encourage The Compiler To Work For You Introduction This tutorial is targeted at the reader who is, perhaps, familiar with the basics of C++ but would prefer a little slower introduction to the more ad…
Programmer's Notepad is, one of the best free text editing tools available, simply because the developers appear to have second-guessed every weird problem or issue a programmer is likely to run into. One of these problems is selecting and deleti…
This tutorial covers a step-by-step guide to install VisualVM launcher in eclipse.
The viewer will be introduced to the technique of using vectors in C++. The video will cover how to define a vector, store values in the vector and retrieve data from the values stored in the vector.
Suggested Courses

926 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question