Re: Newbie question on Ada TExt_IO

[tmoran@acm.org]

> "last" is the size of the string,
  This is true only if Input'first is 1.  ie, if you had
  Input : String(15 .. 237);
and the user entered 2 characters, Last = 16 and Input(15 ..  16), or
Input(Input'first ..  Last), contains the two characters.  It's not a good
habit to assume the first subscript is 1 and Last is the length.  Often a
String has been passed to you as a parameter to a procedure, and the
caller may have passed just a portion of some bigger string, say
  Input : String(1 .. 1024);
  ...
  Input(1 .. 14) := "abcdefghijklmn";
  Some_Procedure(Input(15 .. 237));
Some_Procedure will fail if it assumes its input parameter'first = 1.

>How do you evaluate the length of the string using "Input'Last" isn't always
>going to be 256, it was for me?
  Input'last is the last legal subscript in Input. Given
    Input : String(1 .. 256);
Input'last = 256.  Permanently.  Regardless of the content of Input.
  Last is a variable set by Get_Line that tells the last subscript
Get_Line used to store an input character.  If the user entered no
characters then Get_Line sets Last = Input'first-1 (zero in your
example).  If he entered four characters "5432", then hit the Enter key,
then the '2' goes into Input(4) and Last = 4.