Reading text files

Pls, help me: how can i do this:

I read a text file line-by-line using ifstream.getline();
How can i reposition the pointer so after i read for example 3 lines to start reading from the first line.

Thank you

- open the file again
- store all the lines in an array, accses it after reading

Quote:

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Originally Posted by ElastoManiac

- open the file again
- store all the lines in an array, accses it after reading

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Thank you for the reply but this is not my point, because i have thousands of lines, i don't want to store all the lines in memory. I wonder how can i close the stream or the file and open it again for processing lines from the begining.

any ideea?

What about seekg()?

Step 1 - create the index
- use tellg() to find out where you are in the file
- read a line from the file
- loop until end of file.

Step 2 - use the index
- use seekg() to goto a previous tellg() result
- read the line

Quote:

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Originally Posted by Salem

Step 1 - create the index
- use tellg() to find out where you are in the file
- read a line from the file
- loop until end of file.

Step 2 - use the index
- use seekg() to goto a previous tellg() result
- read the line

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i did like this and didn't works:

Code:

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              // ...
              char s[200];

                ifstream fin;
                fin.open("C:\\in.txt");

                             
                                do {
                                  fin.seekg(0, ios::big);
                                  // read a string from the keyboard...

                                    while(fin.getline(str, 200)) {
                                            // if the string is found then break;
                                    }


                                }while(true); // suppose reading at infinity

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> fin.seekg(0, ios::big);
I thought it was beg, not big?

Also, it needs to be INSIDE the loop with the getline.

Also, you need to store each answer tellg() returns.

What doesn't work?
- it doesn't compile
- it always reads the first line
- it crashes

Quote:

---

Originally Posted by Salem

> fin.seekg(0, ios::big);
I thought it was beg, not big?

Also, it needs to be INSIDE the loop with the getline.

Also, you need to store each answer tellg() returns.

What doesn't work?
- it doesn't compile
- it always reads the first line
- it crashes

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Sorry: was beg, not big.
The positioning don't work simply with seekg(...).
I will try to retrive with tellg...

Thank you very much for the reply.
Best regards!