Reading non-fixed length from binary file

[blackrainbowhu]

Hello!

I'm new here, and I need some help. :)

I am working on a program that has to write and read a binary file. I have to add lectures to it, they look like:

COURSECODE;COURSENAME;MAXAPPLICANTS;ACTUALAPPLICANTS;

I could write that in a file without any problems using char*.

My question is: how do I read that back in a struct if the records are non-fixed size? (e.g.: coursename can be Linear Algebra or Analysis -> length is non-determined) I also need to modify the actual applicants number, how do I find the character position of it, and the current line?

I'd be happy with ideas, and I would appreciate any source code as well, I was programming in C++ and C is a hard step-back for me.

Thank you in advance!

[Banfa]

You have a couple of options.

1. Read the whole line using getline into a std::string and use the various members of std::string to parse the line into the individual data members of your structure
2. Use the delimiter parameter of getline to read up to the ; delimiter in your data lines

[ktsangop]

You can use the following functions :
1. strtok to parse strings seperated by a token (';' in your case).
2. strcmp to compare if two strings are the same.

In a while loop you can use strtok to get each of your records' data and use a counter variable which will be increased every time you find the newline character ('\n').
Using strcmp you can compare each token with the string you are searching. The loop counter will have the line you are positioned in that case.
As for the column of the line you could use strlen on each token and add the lengths of the strings to get the column you are trying to alter.

Hope that helped!

[blackrainbowhu]

How do I use std::string? Isn't that "C++ only"? If I search it in Google I can't really find any C related websites about it, only string methods as you mentioned like strtok and strcmp. Or just make a char* chstring, getline(chstring), and then parse it as you mentioned?

Thanks and sorry for the stupid questions ^^

[ktsangop]

You are correct. Forget about std library, it's c++ not c.
You can look here for a c library reference :
http://www.acm.uiuc.edu/webmonkeys/book/c_guide/

You can look here too
http://www.cplusplus.com/
This is one of the most complete c++ reference websites which of course contains most if not all of C language functions.

All you need to know about is the string library <string.h> and file streams <stdio.h>

[blackrainbowhu]

Thank you very-very much, I owe you a beer I guess. :)

[ktsangop]

No problem..
I'm glad i helped!

[Banfa]

Sorry about that I missed that the thread was in the C not the C++ forum.

Be careful with strtok, it is very non-reentrant and I would avoid it altogether if you are writing a multi-threaded application. You can always do what strtok does with some fairly simple pointer manipulation.

You can read the file line by line with fgets.