From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=0.2 required=5.0 tests=BAYES_00,INVALID_MSGID,
	REPLYTO_WITHOUT_TO_CC autolearn=no autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,c4d884378fc6b03c
X-Google-Attributes: gid103376,public
From: "Norman H. Cohen" <ncohen@watson.ibm.com>
Subject: Re: Two questions
Date: 1996/11/08
Message-ID: <32835AB2.404B@watson.ibm.com>#1/1
X-Deja-AN: 195304120
references: <32825177.41C6@afit.af.mil>
content-type: text/plain; charset=us-ascii
organization: IBM Thomas J. Watson Research Center
mime-version: 1.0
reply-to: ncohen@watson.ibm.com
newsgroups: comp.lang.ada
x-mailer: Mozilla 3.0 (Win95; I)
Date: 1996-11-08T00:00:00+00:00
List-Id: <comp.lang.ada>


Ding-yuan Sheu wrote:

> (1) Is there an easy way to achieve the same result of the C++ sprintf
> function in Ada? 

If you mean causing formatted output going to go to a string instead of
to an output file, the answer is yes, there are versions of Put in the
generic packages Ada.Text_IO.Integer_IO, Ada.Text_IO.Modular_IO,
Ada.Text_IO.Float_IO, and so forth, that take a string rather than a
file as a target.  However, details of formatting are determined by
optional parameters to Put rather than by a printf-style format string. 
Also, there is no Ada analog for C functions with a variable number of
arguments of mixed type.  If x and y are integers and you want to do the
equivalent of
sprintf(s,"%d %d",x,y), you must make two calls on Put and then
concatenate the results (first trimming leading blanks, if this is
important to you):

   Put (X_String, X);
   Put (Y_String, Y);
   Move (S, Trim (X_String, Left) & ' ' & Trim (X_String, Right));
      -- Move and Trim are from Ada.Strings.Fixed
 
> (2) In a C++ function, prorammers can declare a static local variable
> to preserve its value between function calls. Can I do that in Ada?
> For example, in C++, I can write a function as  follows:
> void strcount(char *str)
> {
>    static int total =0;
>    int count = 0;
> 
>    while (*str++) count++;
>    total = total + count;
> }

Unlike C functions, Ada subprograms can be nested in an outer package or
subprogram.  Any variable that is to hold its value from one call on the
subprogram to the next should be declared in a construct surrounding the
subprogram.  For example:

package Character_Counts is
   procedure Count_Characters (Str: in String);
   function Total_Characters return Natural;
end Character_Counts;

package body Character_Counts is

   Total: Natural := 0;  
      -- Hidden from all parts of the program outside this package.
      -- Retains its value between calls on Count_Characters.

   procedure Count_Characters (Str: in String) is
   begin
      Total := Total + Str'Length;
   end Count_Characters;

   function Total_Characters return Natural is
   begin
      return Total;
   end Total_Characters;

end Character_Counts;

This example is not all that different from declaring a static variable
at the file level in C, but Ada also provides more flexibility, e.g.
declaring several subpackages in a single file to minimize the region of
the program in which the variable is visible, or enclosing a variable in
a surrounding SUBPROGRAM (in which case the variable holds its value
between calls on the inner subprogram that occur during one call on the
outer subprogram, but the variable ceases to exist each time the outer
subprogram returns).

-- 
Norman H. Cohen
mailto:ncohen@watson.ibm.com
http://www.research.ibm.com/people/n/ncohen