錯誤修正：提出CONSTRAINT_ERROR：book1.adb：28長度檢查失敗

Question

我試圖用Ada做的是創建一個Book對象，然後打印出那本書。問題是，該語言不是很可寫。當我編譯，生成的主要文件，然後執行該文件，它給了我這個錯誤：

raised CONSTRAINT_ERROR : book1.adb:28 length check failed 

這裏就是我在體內文件：

package body Book1 is 

function getAuthor (B: in Book) return AuthorName is 

begin 
    return B.getAuthor; 
end getAuthor; 

function getTitle (B: in Book) return TitleName is 

begin 
    return B.getTitle; 
end getTitle; 

function getNumberOfPages (B: in Book) return Pages is 

begin 
    return B.getNumberOfPages; 
end getNumberOfPages; 

function createBook (Author: in String; Title: in String; NumberOfPages: in Float) 
        return Book is 
    B: Book; 

begin 
    B.getAuthor := Author; 
    B.getTitle := Title; 
    B.getNumberOfPages := NumberOfPages; 
    return B; 
end createBook; 

end Book1; 

下面是我在spec文件：

package Book1 is 

type Book is tagged private; 

subtype AuthorName is String (1 .. 300); 
subtype TitleName is String (1 .. 750); 
subtype Pages is Float range 0.0 .. 5000000.0; 

function getAuthor(B: in Book) return AuthorName; 

function getTitle(B: in Book) return TitleName; 

function getNumberOfPages(B: in Book) return Pages; 

function createBook(Author: in String; Title: in String; NumberOfPages: in Float) 
        return Book; 

private 
    type Book is tagged 
    record 
    getAuthor: AuthorName; 
    getTitle: TitleName; 
    getNumberOfPages: Pages; 
    end record; 

end Book1; 

下面是我在測試文件：

with Book1, Ada.Text_IO, Ada.Float_Text_IO; 
use Book1, Ada.Text_IO, Ada.Float_Text_IO; 

procedure testBook is 

theRealBook: Book := createBook(Author => "Jordan White", 
             Title => "The Last Christmas", 
             NumberOfPages => 32.0); 

procedure Print_Book (B: in Book'Class) is 

begin 
    Put (getAuthor (B => B)); 
    Put (getTitle (B => B)); 
    Put (getNumberOfPages (B => B)); 
    New_Line; 
end Print_Book; 

begin 
Print_Book (theRealBook); 

end testBook; 

我究竟在做什麼來獲得這個錯誤，我該如何解決？

Answer 1

你在這裏的講話：

theRealBook: Book := createBook(Author => "Jordan White", 
             Title => "The Last Christmas", 
             NumberOfPages => 32.0); 

具有這兩個作者和標題（字符串）中字符串的長度隱。 這意味着，當你在這裏指定作者和書名：

B.getAuthor := Author; 
    B.getTitle := Title; 

您正在假設「喬丹白」是一個長度爲300（標題爲同樣的問題）的字符串 我懷疑這是功課，所以生病讓你想出如何找到長度和字符串的界限，以及如何分配數組片。