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Internet Message Format | 1996-08-05 | 2.7 KB

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From: [e-mail] (Brian V. McGroarty)
Newsgroups: comp.lang.c
Subject: Re: array of struct
Date: 20 Mar 1996 14:18:44 GMT
Organization: Internet Squire
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I'll assume that pointers to the strings are okay, i.e. you don't need them
to be an actual part of the structure.

I would allocate a pool of RAM which is one character larger than the file.
 By running through this range of memory and replacing all line ends with
character 0 you create a table of individual strings.  During the run
through the file where you were replacing line ends you could either count
the number of strings to determine how many structures you will need to
allocate in an array, or you could count as well as place pointers to the
beginning of each string in a temporary array of pointers which is
guaranteed to be large enough to hold the entire set of pointers.  If you
have simply counted then you must run through the file again to fill the
member of each structure which should contain a pointer to a string.  If
you have created the temporary array of pointers then you would copy these
pointers from the array instead.

Something else which I see people do from time to time is to allocate an
array of items which is guaranteed to be large enough to hold a full set
and resize with realloc() or to create a linked list, resulting in a new
allocation for every single record.  I don't like the realloc() method
because it temporarily bloats your program's memory requirements and, thus,
causes some virtual memory systems to thrash.  A linked list is a good
answer if you will be dynamically adding or removing data items, but it
reduces the speed of random access to your data and adds extra
inefficiencies due to the system's internal structuring of your memory list
and on systems which allocate objects of a multiple of a certain size.


Lawrence O'Leary wrote:

>I have a question... though it is petty it bothers me greatly.  :(

>How would I create a runtime defined array of struct.

>What I want to do is create each record in the array by reading a line
>from a file and storing each field of the line into the record.  Do this
>for every line in the file and then where done.  What I need to do is
>create the array of the struct for the exact number of lines that are in
>the file.  This way I won't be wasting memory and I won't have to worry
>about not having enough records to store the lines into.

---
Brian Valters McGroarty -- [e-mail]
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