Question

我有程序来读取通用包，但是我无法弄清楚如何处理上下文子句以获取要打印和/或从文件中读取的数字。在目前的客户端程序中，我认为Element_Type应该是一个整数，但我的所有声明都是类型元素，当没有Ada.Element_text_IO时，我该怎么做呢？请让我知道，我已经被困了很长一段时间。

客户端程序

WITH Ada.Text_IO; 
WITH Ada.Integer_Text_IO; 
WITH Ada.Float_Text_IO; 
WITH Min_Max;

PROCEDURE Min_Max_Average_File IS
------------------------------------------------------------------
--| Finds and displays the minimum, maximum, and average
--| of a list of data items; the data items are read from a file.                                   
------------------------------------------------------------------

package Grades is new Min_Max(Element_Type => Integer);
use Grades;



  NumValues:    Element;  -- input - the number of items to be averaged
  CurrentValue: Element;   -- input - the next data item to be added   
  Smallest:     Element;   -- output - minimum of the data values
  Largest:      Element;   -- output - maximum of the data values
  Average:      Element;   -- output - average of the data values
  Sum:          Element;   -- program variable - the sum being accumulated   
  TestScores:   Ada.Text_IO.File_Type; 

BEGIN  -- Min_Max_Average_File
  -- Open the file and associate it with the file variable name
  Ada.Text_IO.Open
    (File => TestScores, Mode => Ada.Text_IO.In_File, Name => "scores.txt");

  -- Read from the file the number of items to be averaged
           Ada.Integer_Text_IO.Get(File => TestScores, Item => NumValues);  
           Ada.Text_IO.Put("The number of scores to be averaged is ");
           Ada.Integer_Text_IO.Put(Item => NumValues, Width => 1);  
           Ada.Text_IO.New_Line;
  -- Initialize program variables
  Smallest := Element'Last;
  Largest := Element'First;
  Sum := 0;

  -- Read each data item, log to the screen, add it to Sum, 
  -- and check if it is a new minimum or maximum
  FOR Count IN 1 .. NumValues LOOP
    Ada.Integer_Text_IO.Get(File => TestScores, Item => CurrentValue);
    Ada.Text_IO.Put("Score number ");
    Ada.Integer_Text_IO.Put(Item => Count, Width => 1);  
    Ada.Text_IO.Put(" is ");
    Ada.Text_IO.Put(Item => CurrentValue, Width => 1);  
    Ada.Text_IO.New_Line;
    Sum := Sum + CurrentValue;
    Smallest := Grades.Minimum(Value1 => Smallest, Value2 => CurrentValue);
    Largest  := Grades.Maximum(Value1 => Largest,  Value2 => CurrentValue);

  END LOOP;

  -- compute the average; since Sum and NumValues are integers,
  -- the average is truncated, that is, the fractional part is discarded
  Average := Sum / NumValues;

  -- display the results
  Ada.Text_IO.Put(Item => "The Smallest is ");
  Ada.Integer_Text_IO.Put(Item => Smallest, Width => 1);  
  Ada.Text_IO.New_Line;
  Ada.Text_IO.Put(Item => "The Largest is ");
  Ada.Integer_Text_IO.Put(Item => Largest, Width => 1);  
  Ada.Text_IO.New_Line;
  Ada.Text_IO.Put(Item => "The Average is ");
  Ada.Integer_Text_IO.Put(Item => Average, Width => 1);  
  Ada.Text_IO.New_Line;

END Min_Max_Average_File;

包规范

generic

  Type Element_Type is private;


PACKAGE Min_Max IS

------------------------------------------------------------------
--| specifications of functions provided by Min_Max package                                     
------------------------------------------------------------------
  Type Element is new Element_Type;
  FUNCTION Minimum (Value1, Value2: Element_Type) RETURN Element_Type;
  -- Pre:  Value1 and Value2 have been assigned values
  -- Post: Returns the smaller of the two input values

  FUNCTION Maximum (Value1, Value2: Element_Type) RETURN Element_Type;
  -- Pre:  Value1 and Value2 have been assigned values
  -- Post: Returns the larger of the two input values

包体

PACKAGE BODY Min_Max IS
------------------------------------------------------------------
--| bodies of functions provided by Min_Max package                                     
------------------------------------------------------------------

  FUNCTION Minimum (Value1, Value2: Element_Type) RETURN Element_Type IS
    Result: Element_Type;
  BEGIN

    IF Value1 < Value2 THEN
       Result := Value1;
    ELSE
       Result := Value2;
    END IF;
    RETURN Result;

  END Minimum;

  FUNCTION Maximum (Value1, Value2: Element_Type) RETURN Element_Type IS
    Result: Element_Type;
  BEGIN

    IF Value1 > Value2 THEN
       Result := Value1;
    ELSE
       Result := Value2;
    END IF;
    RETURN Result;

  END Maximum;

END Min_Max;

Answer 1

当我尝试编译Min_Max的规范时，收到错误消息：

min_max.ads:16:71: missing "end Min_Max;"

修复这应该是非常简单的。

Answer 2

当你说

时

package Grades is new Min_Max(Element_Type => Integer);

这意味着Grades的功能属于Min_Max，代表Integers 。

因此，您不应声明类型为NumValues的{{1}}等，而应声明Element类型。这将解决您能够读/写值的问题。

但是，编译泛型时会遇到问题。您已将Integer声明为Element_Type;这限制了您可以对此类型的对象执行分配和等同性比较。它确实不支持＆＃34;＆lt;＆＃34;，＆＃34;＆lt; =＆＃34;，＆＃34;＆gt; =＆＃34;，＆＃34; ＆GT;＆＃34;

如果您愿意支持有符号整数类型，可以说（ARM 12.5.2(3)）

private

或者（假设您也希望能够支持浮点类型），您需要导入相关操作（ARM 12.6(18)）：

type Element_Type is range <>;

（type Element_Type is private; with function "<" (L, R : Element_Type) return Boolean is <>; with function ">" (L, R : Element_Type) return Boolean is <>;表示使用具有相同名称的is <>操作（如果有）。

如何使这个通用包编译

2 个答案: