CODEWITHSUNDEEP
c++file
dann_
dann_

Reputation: 47

seekp not going to required position

In this program i want to change some value in the file.Now i am opening the file in append mode and moving my seekp pointer to my given location.But the problem is that it is writing data at the end of file not there where the seekp pointer is there. 

#include<iostream>
#include<fstream>
using namespace std;
int main(){

//creates a file for testing  purpose.  
    ofstream fout;
    fout.open("test.txt");
    fout<<1;
    fout<<" ";
    fout<<34;
    fout<<" ";
    fout<<-1;
    fout<<" ";
    fout<<-1;
    fout.close();

//reads the data in the file    
    ifstream fin;
    fin.open("test.txt");
    fin.seekg(0,ios::beg);
    fin.unsetf(ios::skipws);//for taking whitespaces
    char sp;
    int item;
    fin>>item;
    while(!fin.eof()){
    cout<<item<<endl;
    fin>>sp;//to store whitespaces so that fin can take next value
    fin>>item;  
    }
    cout<<item<<endl;
    fin.close();

//opening file for editing
    fout.open("test.txt",ios::app);
    fout.seekp(5,ios::beg);
    fout<<3;
    fout.close();
    return 0;
}

Upvotes: 1

Views: 885

Answers (1)

Some programmer dude
Some programmer dude

Reputation: 409166

If you read e.g. this reference you will see that std::ios::app means

seek to the end of stream before each write

So it doesn't matter where you seek, all writes will be done at the end of the file.

The best way to modify a file is to read it into memory, then rewrite it to a temporary file, and then move the temporary file over the original file.

Upvotes: 2

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