Wvsprintf in Ada

Wvsprintf in Ada

[EMANUELE COSTA]

Hello everybody,
        I'm trying to convert the programs which appear in the book
"Programming Windows" by Peztold from C to Ada, and I've encountered a
curious problem with the use of the Win32 api function Wvsprintf.
        Actually the function is supported within the Alsys Activada
compiler throughout the call to the pragma CALL_IN, but it doesn't seem
to work in the same way as the C function does.
        Here is an example:
if we had the following code in C:

        short nLength;
        char szBuffer[40];
        nLength = wvsprintf(szBuffer,"The sum of %d and %d is %d",
        nA,nB,nA+nB);
        Textout(hdc,x,y,szBuffer,nLength);

and we wrote down the following Ada code:

        nLength         : integer;
        szBuffer1       : string(1..100);
        szBuffer2       : constant string := "The sum of %d and %d is %d" &
        ascii.null;
        nLength:=wvsprintf(szBuffer1'address,szBuffer2'address,nA,nB,nA+nB);
        Textout(hdc,x,y,szBuffer1,nLength);

we 'll finished with this compiling time error:

        No Valid prefix is compatible with this list of indexes or of
        parameters.

The unique solution I've worked out so far is to declare an array to
store all the integers I need to perform the sum, and assuming that all the
numbers will be stored in adjacent memory locations we have got the
following code:

        nLength         : integer;
        szBuffer1       : string(1..100);
        szBuffer2       : constant string := "The sum of %d and %d is %d" &
        ascii.null;
        type number is array (1..3) of integers;
        sum_numbers     : number;
        sum_numbers(1) := 2;
        sum_numbers(2) := 3;
        sum_numbers(3) := sum_numbers(1) + sum_numbers(2);
        nLength:=wvsprintf(szBuffer1'address,szBuffer2'address,sum_numbers'
        address);
        Textout(hdc,x,y,szBuffer1,nLength);

and peculiarly enough the program seems to work fine and at the end a
window is displayed on the screen with the correct output.
        The only thing is that  the whole procedure looks quite
clumsy, so I would like to know if there is someone who can help me and
perhaps suggest a better solution to this problem.
        Thanks a lot
                        EMANUELE COSTA

======================
Emanuele Costa
Pendle College
Lancaster University

costa@unix.lancs.ac.uk
======================

Re: Wvsprintf in Ada

[Mitch Gart]

In the Win32Ada binding available at 
http://sw-eng.falls-church.va.us/AdaIC/source-code/bindings/
the binding to this function is

    function wvsprintf(lpOut  : Win32.LPSTR;
                       lpFmt  : Win32.LPCSTR;
                       arglist: Stdarg.ArgList := Stdarg.Empty)

The key to it is the Stdarg package which handles variable-length
argument lists, and which is included as part of the binding.
The binding is Ada 95.  Hope that helps.

- Mitch Gart