I hope I have read your message correctly, because your question seems a
bit odd to me (as your message comes from someone who knows the PIC
architecture so well).  So, I pray I haven't missed something that takes
this from a beginning 'C' question to advanced syntax/semantics.

When you initialize a structure, you must remember that strings are not
a primitive type in 'C'.  What you want to happen is for the strings to
get copied from an element of the messages array to your struct members.
Unfortunately, you can't do it without code in 'C'.

A better construct is to have macro definitions for the strings and have
the messages buffer elements AND the display_type_frames[] elements
initialized from the macros.  Like this:

#define MY_MSG_SPLASH "Greenkeeper v"
#define MY_MSG_ERR "Error"

char **messages = {
        MY_MSG_SPLASH,
        MY_MSG_ERR
};

SomeVarType_t display_type_frames[] = {
        {
                0x81,
                MY_MSG_SPLASH,
        },
        {
                0x86,
                MY_MSG_ERR,
        }
};

If the strings change dynamically, there is no substitute for a function
that initializes your display_type_frames elements.

What you were doing with this code:

SomeVarType_t display_type_frames[] =
{
        {
                0x81,
                *messages[splash],
        }
}

is equivalent to putting a character in the second member, just as you
discovered.

This is because of how the pointers work.  You have to use the operators
in prececence.  The messages variable is of type "char **", which is a
list of pointers.  Each pointer points to a list of characters.

First precedence is the [] operator.  That takes "char **" and goes to
"char *" (getting some element of an array pointed to by the "char **"
array).  The index in the your first example is "splash" which I'm not
sure is a constant or a variable (I didn't read the prior messages,
oops!).

The "*" operator comes next, and it does the same thing but it evaluates
to the first element pointed to by the pointer.  So, you go from "char
*" to "char".

Brian

-----Original Message-----
I've discovered that I have some form of 'pointing 'problem, if I
replace the  struct like so - everything works

display_type frames[3]={

  {
   0x81,
   //*messages[splash]
   "Greenkeeper v"
  },

  {
   0x86,
   //*messages[err]
   "Error"
  },

  {
    0xC0,
    //*messages[set]
    "Time"
  }
};

If I replace the actual strings back to the *messages[x] then what I
get is only the first character of the string, and no amount of
persuading seems to alter this, even if I try and copy the sub array
into a temporary buffer and then use that to copy into the display
buffer - which also seems a very long winded and inelegant way to
accomplish this.

The main calling code is now
{

strcpy(DisplayBuffer+1,&frames[index].display_no[0]);
DisplayBuffer[0]=frames[index].position[0];
display(DisplayBuffer);

}

Where index decides which frame within the frames array is to be
used. The hard coded zero is so that each part of the array starts at
the first character.

I also found that to get this to work I had to change the first
struct to

struct display_type
{
    unsigned char position[1];
    unsigned char display_no[14]; //THIS CHANGED FOR LEN OF MAX SIZE
in *messages[].

}

So I'm almost there, I could compromise and just use the code as it
stands, but I hate being defeated with problems, and the whole idea
was to make the menu code more portable between projects and easier
to maintain.

And before anyone points out that DisplayBuffer is not how I've
written the other labels, this is because this label was produced by
the Renesas project generator, and I just haven't changed it to my
style.

Colin
--
cdb, bodgy1@optusnet.com.au on 29.11.2003

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