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Re: Program to extract a substring from a string; compiling issues

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Alla _ <modelling.data@gmail.com> writes:

>> >     subword [] = substring (word, start_letter, count_number);
>> 
>> You can't assign to an array in C, if that is what you are trying to do
>> (that would look more like subword = substring(...) so maybe that's not
>> what you are trying).
>> 
>> Pretty much the only viable option here is to pass into substring a
>> pointer to the (start of) the array into which the substring should be
>> copied.
>> 
> Unfortunately, I don't understand this part. I don't see
> how this functions differs from the function in the below
> program (copied from the book), which doesn't return
> anything as well.

<snip>
> void read_line (char buffer [], int size);

Indeed not.  This function does exactly what I'm saying you need to do.
Here, buffer is a pointer to the start of an array of char.  The
function fill the array with data read from the input stream.

You substring function needs another parameter which will be a pointer
to the array where it should copy the character of the requested
sub-string.

<snip>
>> > void substring (char source[], int start, int count)
>> > {
>> >     int i;
>> >     char result [80];
>> 
>> Why 80?  You can't know know that 80 is enough, but if you've picked a
>> size for an array, make sure you check that it is enough.  Either refuse
>> to do anything if count >= 80, or only put a maximum of 79 characters
>> and a null into it.
>> 
> The book says that 80 is a standard width of the terminal :)
> Actually, 80 is my mistake, corrected it to 81 to account for
> a null character.

OK, so you've explained why you pick that number (and I knew that too to
be honest -- it was a rhetorical question) but do you understand the
rest?  It's very important to know why it's wrong to ignore an array's
size.
>
>> >     if (count > string_length (source))
>> 
>> This is not a useful test.  See below.
>> 
>> >     {
>> >         for (i = start; i <= (start + count) && source[i] != '\0'; i++)
>> >         {
>> >             result [i] = source [i];
>> 
>> So if start is 17, i starts at 17 and this does result[17] =
>> source[17].  Is that what you want?
>> 
>> >         }
>> >         result [i + 1] = '\0';
>> >     }
>> >     else
>> >     {
>> 
>> Here we know that count <= string_length(source) but that's not really
>> very useful to know.  If the length is 100 and start is 99 even a count
>> of 10 goes wrong.
>> 
>>
> Corrected :)
> int i;
>     char result [81];
>     
>     if (count > string_length (source))
>     {
>         for (i = start - 1; i <= (start - 1 + count) && source[i] != '\0'; i++)
>         {
>             result [i] = source [i];
>         }
>         result [i + 1] = '\0';
>     }
>     else if (count < string_length (source) && start >= 1 && start <= (length - count))
>     {
>         for (i = start - 1; i <= (start - 1 + count); i++)
>         {
>             result [i] = source [i];
>         }
>         result [i + 1] = '\0';
>     }

No, not corrected, just changed!

There's a lot more wrong with this version than the previous one, but
picking at it like a crow at road kill won't help anyone.

Here's another way to think about this where you won't be side-tracked
by the source length.  You are sitting opposite me at a table.  I have a
stack of playing cards and I ask you to put the 6 cards starting with
the 3rd onto the table in front of you.  You can ask me for the next
card, but that's all.  Every time you do I give you the next card or I
hold my hand up and say "null -- there is no next card".  How do you
proceed?

-- 
Ben.

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Program to extract a substring from a string; compiling issues Alla _ <modelling.data@gmail.com> - 2015-10-14 03:24 -0700
  Re: Program to extract a substring from a string; compiling issues Bartc <bc@freeuk.com> - 2015-10-14 11:49 +0100
    Re: Program to extract a substring from a string; compiling issues Alla _ <modelling.data@gmail.com> - 2015-10-14 05:17 -0700
      Re: Program to extract a substring from a string; compiling issues Bartc <bc@freeuk.com> - 2015-10-14 13:31 +0100
        Re: Program to extract a substring from a string; compiling issues Jorgen Grahn <grahn+nntp@snipabacken.se> - 2015-10-14 13:40 +0000
        Re: Program to extract a substring from a string; compiling issues Alla _ <modelling.data@gmail.com> - 2015-10-14 07:46 -0700
  Re: Program to extract a substring from a string; compiling issues Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-14 13:42 +0100
    Re: Program to extract a substring from a string; compiling issues Alla _ <modelling.data@gmail.com> - 2015-10-14 08:14 -0700
      Re: Program to extract a substring from a string; compiling issues Keith Thompson <kst-u@mib.org> - 2015-10-14 11:23 -0700
      Re: Program to extract a substring from a string; compiling issues Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-14 21:22 +0100

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