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C++ read file from .txt and holds the desired value in a new .txt using Xcode...

Answer 1

+1 A:

Read a line and discard it. Read the next line and break it into fields, keeping the third and fourth. Read the next 6 lines and discard them to get ready for the next record.

Jerry Coffin 2010-10-15 19:24:05

I'm sorry but I'm quite new with C++. It's for my uni project. A code would pretty much help me...

Kunta 2010-10-15 19:28:57

@Kunta: To read a line, you'd typically use `std::readline`. To read fields, you'd put the line into an `std::istringstream`, and then use `line >> field1 >> field2 >> field3 >> field4;`. For simplicity, you can define all the fields as `std::string`s. Just to be clear: while I'm happy to give advice about how to write the code, I'm *not* going to write the code for you.

Jerry Coffin 2010-10-15 19:44:56

Thank you. I am trying to write the code now and will ask if there's any error...

Kunta 2010-10-15 19:52:50

Answer 2

A:

Come on. Who uses C++ for that? It is a one-line awk command:

awk '/^[ \t]/ { printf("%s\t%s\n", $3, $4); }' file.txt

Vlad Lazarenko 2010-10-15 19:37:47

If you're going to use awk, you can make it a lot simpler still. If I'm not mistaken, something like: `"/^ [0-9]/ { print $3 $4; }"` should do the job.

Jerry Coffin 2010-10-15 19:41:29

@Jerry: that will try to match the whole line... so there will be no matches. I bet awk alone can do it, but I don't know it enough to write a complex scripts :)

Vlad Lazarenko 2010-10-15 19:47:18

I'm using C++ because later I'm going to visualize the IP address into maps using OpenGL...

Kunta 2010-10-15 19:50:18

So pre-process this file with the shell script and feed your C++ application with normalized data so it doesn't have to parse anything.

Vlad Lazarenko 2010-10-15 19:51:47

@Vlad: Not so. In fact, given that it's the only line starting with whitespace, you can simplify it even more: `awk "/^[ \t]/ { printf(\"%s\t%s\n\", $3, $4; }" addresses.txt` Doing a quick test, it looks like it's actually using a tab, so the previous one won't work (though the fix is trivial).

Jerry Coffin 2010-10-15 19:54:04

@Jerry: That will work, I've replaced my ugly stuff with this awk-only solution.

Vlad Lazarenko 2010-10-15 19:57:24

@Vlad: Why not do it in C++ like so: `system("awk '/^[ \t]/ { printf("%s\t%s\n", $3, $4); }' file.txt");`?

thyrgle 2010-10-15 23:40:29

how do i use awk in C++??

Kunta 2010-10-15 23:57:26

@thyrgle Because you cannot capture the output of `system`. It returns exit code. In order to capture the output, you have to fork the process, dupe descriptors, exec the bash with `-c` and command. It is a long story and I find combining scripts with `C++` easier than writing all in `C++`. Not to mention that `readline` plus a couple of `find_first_of` on `std::string` is much easier. But, you know, I don't think this is a place where people write code for you.

Vlad Lazarenko 2010-10-16 02:50:10

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