Re: data structures

From: d. hall (dhall@APK.NET)
Date: 01/22/98

// thus on Tue, 20 Jan 1998 15:02:22 -0500, Jamie virtually wrote:

> Antioch wrote:

>> Ok, so i've come across this thing that i can't identify in any of my C
>> books and my head's starting to hurt from banging it on the wall:

>> char **list_of_something;

>> Looking through the code, it seems to store arrays of strings. However,
>> I'm trying to figure out why they used something like this instead of
>> creating a structure or just a regular character array.

>> Can anyone identify this little deal and explain its usefullness?  I would
>> appreciate it very very very very very very very much.

> You're right in that it is an array of strings, or more accurately an
> array of pointers to chars.  This would be equivalent to writing the
> following:

>         char *list_of_something[];

No it wouldn't, although C has the equivalence of arrays and pointers, do
not confuse them as such (comp.lang.c FAQ).

        char **data

        This is a pointer to a pointer of type char.

        char *data

        This is a pointer of type char (also known as a string).

char **data is normally used to make a 2 dimensional array.

  data points to this            ,--> **data
          |                     /   ,--> *(*data + 1)
          V                    /   /
        [PTR] *data -------> [f] [i] [r] [s] [t] [\0]
        [PTR] *(data + 1) -> [s] [e] [c] [o] [n] [d] [\0]
        [PTR] *(data + 2) -> [t] [h] [i] [r] [d] [\0]

char *data[] is an array of pointers of type char, it is only when you feed
this to a function does it become a pointer to a pointer of type char.


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