NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c-part1/9360

Internet Message Format | 1996-08-05 | 1.9 KB

Path: lrz-muenchen.de!news
From: [e-mail] (Kurt Watzka)
Newsgroups: comp.lang.c
Subject: Re: Q: How to assign structures?
Date: 9 Mar 1996 19:45:52 GMT
Organization: Leibniz-Rechenzentrum, Muenchen (Germany)
Distribution: world
Message-ID: <4hsn5g$[e-mail]>
References: <4gsalu$[e-mail]> <4hse0f$efq@SNFC21_SRVR_WWW.PBI.net>
NNTP-Posting-Host: sun2.lrz-muenchen.de

[e-mail] writes:

>In <4gsalu$[e-mail]>, [e-mail] (Toby K Hay) writes:
>>I need to assign values to structures in one array from structures in
>>another array - in essence I'm copying the whole structure from one array
>>to the other.  Can I use simple assignment like this:

>>struct StructName {
>>    int     IVal;
>>    float    FVal;}

>>struct StructName Array1[5], Array2[5];
>>.. . .
>>for (i=0;i<5;i++) Array1[i] = Array2[i];
>>.. . .
>>And if not that, can I use memcpy() and sizeof() to do the assignment:

>>for (i=0;i<5;i++) memcpy(&Array2[i],&Array1[i],sizeof(struct StructName));
>>Or do I have to assign each element of the structure?

>It would be a lot easier to create a pointer to the struct and then make a copy
>of the pointer;

I beg to differ. Copying pointers is _not_ equivalent to copying values.
Consider an algorithm that will change the contents of the array
of structures. Since you want to _keep_ the original values as well,
what would you do using your approach?

It _may_ be useful to pass a pointer to a struct to a function instead
of the whole struct, but sometimes you just _need_ the call by value
semantics that C uses in all function calls.

>struct mystruct {..} ms, *ps;

>main()
>{
>    void *ns;

Why on earth do we need a void * in this program.

>    ps = &ms;
>    ns = ps;
>}

Kurt
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