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Asked: 2026-05-10T21:14:46+00:00

I want to be able to read from an unsorted source text file (one

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I want to be able to read from an unsorted source text file (one record in each line), and insert the line/record into a destination text file by specifying the line number where it should be inserted.

Where to insert the line/record into the destination file will be determined by comparing the incoming line from the incoming file to the already ordered list in the destination file. (The destination file will start as an empty file and the data will be sorted and inserted into it one line at a time as the program iterates over the incoming file lines.)

Incoming File Example:

1 10/01/2008 line1data 2 11/01/2008 line2data 3 10/15/2008 line3data

Desired Destination File Example:

2 11/01/2008 line2data 3 10/15/2008 line3data 1 10/01/2008 line1data

I could do this by performing the sort in memory via a linked list or similar, but I want to allow this to scale to very large files. (And I am having fun trying to solve this problem as I am a C++ newbie :).)

One of the ways to do this may be to open 2 file streams with fstream (1 in and 1 out, or just 1 in/out stream), but then I run into the difficulty that it’s difficult to find and search the file position because it seems to depend on absolute position from the start of the file rather than line numbers :).

I’m sure problems like this have been tackled before, and I would appreciate advice on how to proceed in a manner that is good practice.

I’m using Visual Studio 2008 Pro C++, and I’m just learning C++.

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1 Answer

  1. The basic problem is that under common OSs, files are just streams of bytes. There is no concept of lines at the filesystem level. Those semantics have to be added as an additional layer on top of the OS provided facilities. Although I have never used it, I believe that VMS has a record oriented filesystem that would make what you want to do easier. But under Linux or Windows, you can’t insert into the middle of a file without rewriting the rest of the file. It is similar to memory: At the highest level, its just a sequence of bytes, and if you want something more complex, like a linked list, it has to be added on top.

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