Copying a file multiple times using loop; C/C++

Question

I wanted to copy a file multiple times using different names.

The program is this:

#include<iostream>
#include<cstdio>
#include<cstdlib>
#include <sstream>
#include<cstring>
using namespace std;

main()
{
    string text;
    int i;
    char ch;
    ostringstream oss;
    FILE *fp1,*fp2;
    if((fp1=fopen("One Dollar.jpg", "rb"))==NULL)
    {
        cout<<"Error";
        exit(-1);
    }
    for(i=1; i<=5; i++)
    {
        oss << "C:\\5241 Dollar\\One Dollar " << i << ".jpg";

        text = oss.str();

        if((fp2=fopen(text.c_str(), "wb"))==NULL)
        {
            cout<<"Error "<<i;
            exit(-1);
        }
        while(!feof(fp1))
        {
            fread(&ch, 1, 1, fp1);
            fwrite(&ch, 1, 1, fp2);
        }

        fclose(fp2);

       /* for(int j=0;j<30000;j++)
            for(int k=0;k<30000;k++)
                if(k==3000)
                    cout<<k; */

    }
    fclose(fp1);
}

In this there are two file streams one of which is source and the other is destination.. I loaded the actual file in binary read mode and the destination as binary write mode. I used a for loop to do the work. But as soon as the loop iterates 2nd time, the file opening of fp2 fails. I'm getting the output: Error 2.

How can I make the code work?

Actually it's not an error, i.e the compiler doesn't show any error. by Bad. It's probably a bug... 2nd time, I get the output: Error 2 from this if statement: if((fp2=fopen(text.c_str(), "wb"))==NULL) — ponir, Sep 25 '11 at 13:48
You are using C++ classes. Why not to use `fstream` instead of C file functions? — Griwes, Sep 25 '11 at 14:06
@Griwes none of the issues in this question would be solved by switching to C++ file constructs — Foo Bah, Sep 25 '11 at 16:01
@FooBah, it was just a suggestion, that's why it's here, not in the answers. — Griwes, Sep 25 '11 at 19:13

Foo Bah · Accepted Answer · 2011-09-25T14:05:05.133

You should open and close the first file in each iteration of the loop.

....
for(i=1; i<=5; i++)
{    
    if((fp1=fopen("One Dollar.jpg", "rb"))==NULL)
    {
        cout<<"Error";
        exit(-1);
    }
....

The reason is because at the end of the first iteration, the first file pointer is at the end of the file, so it won't see any data at the second iteration. You have to close and reopen the file (OR you can use seek to jump to the front of the file, but this is the simpler change since its a copy-and-paste)

EDIT: to the new question:

you need to reset the stringstream. In the second iteration you are trying to open

C:\\5241 Dollar\\One Dollar 1.jpgC:\\5241 Dollar\\One Dollar 2.jpg

which is invalid.

One solution is to bring the ostringstream declaration into the loop:

....
for(i=1; i<=5; i++)
{    
    if((fp1=fopen("One Dollar.jpg", "rb"))==NULL)
    {
        cout<<"Error";
        exit(-1);
    }
    ostringstream oss;
    oss << "C:\\5241 Dollar\\One Dollar " << i << ".jpg";

This solves another problem That I haven't considered yet. Thatnks for that. But the problem I was having remains. In output I get: Error 2 which means, in this if((fp2=fopen(text.c_str(), "wb"))==NULL) { cout<<"Error "< — ponir, Sep 25 '11 at 13:41

score 0 · Answer 2 · answered Dec 22 '16 at 19:43

0

int main()
{
    string text;
    int i;
    char ch;
    ostringstream oss;
    FILE *fp1,*fp2;

    if((fp1=fopen("/home/maru/fact.cpp", "rb"))==NULL)
    {
        cout<<"Error";
        exit(-1);
    }

    for(i=1; i<=5; i++)
    {
        oss << "/home/maru/fact" << i << ".cpp";
        text = oss.str();

     rewind(fp1);

     cout<<text<<"\n";

     if((fp2=fopen(text.c_str(), "wb"))==NULL)
        {
            cout<<"Error "<<i;
            exit(-1);
        }

        while(!feof(fp1))
        {
            fread(&ch, 1, 1, fp1);
            fwrite(&ch, 1, 1, fp2);         
        }

       fclose(fp2);
       oss.str("");

    }
    fclose(fp1);
    return 0;
}

answered Dec 22 '16 at 19:43

vishnu

1

2

Please, add some comments in your answer or directly to your source code to explain why your solution matches with the question. – J. Piquard Dec 22 '16 at 20:18
1

And also read [Why is “while ( !feof (file) )” always wrong?](http://stackoverflow.com/questions/5431941/why-is-while-feof-file-always-wrong) The code you posted will write the last character read from `fp1` to `fp2` *twice*. – Andrew Henle Dec 22 '16 at 20:25

Copying a file multiple times using loop; C/C++

2 Answers2