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
328 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 50 total points
Comment Utility
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 75 total points
Comment Utility
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 75 total points
Comment Utility
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 45

Assisted Solution

by:Kdo
Kdo earned 50 total points
Comment Utility
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

What Security Threats Are You Missing?

Enhance your security with threat intelligence from the web. Get trending threat insights on hackers, exploits, and suspicious IP addresses delivered to your inbox with our free Cyber Daily.

Join & Write a Comment

Introduction This article is the first in a series of articles about the C/C++ Visual Studio Express debugger.  It provides a quick start guide in using the debugger. Part 2 focuses on additional topics in breakpoints.  Lastly, Part 3 focuses on th…
Introduction This article is a continuation of the C/C++ Visual Studio Express debugger series. Part 1 provided a quick start guide in using the debugger. Part 2 focused on additional topics in breakpoints. As your assignments become a little more …
The viewer will learn how to clear a vector as well as how to detect empty vectors in C++.
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.

771 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

Need Help in Real-Time?

Connect with top rated Experts

10 Experts available now in Live!

Get 1:1 Help Now