Difference between revisions of "Basic Pascal Tutorial/Chapter 4/Forward Referencing/zh CN"

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{{Basic Pascal Tutorial/Chapter 4/Forward Referencing}}
  
 
4F - 前向引用 (原作者: Tao Yue, 状态: 未更改)
 
4F - 前向引用 (原作者: Tao Yue, 状态: 未更改)
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如:
 
如:
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procedure Later (参数列表); forward;
 
procedure Later (参数列表); forward;
  
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示例:
 
示例:
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program q;
 
program q;
  
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[[Category: Object Pascal Introduction]]
 
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Latest revision as of 15:20, 20 August 2022

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4F - 前向引用 (原作者: Tao Yue, 状态: 未更改)

这些虽然容易理解,但有时也让人困惑。

程序中只能使用已经定义的过程/函数?或许是这样吧,先定义后使用。

不过,也有例外,你想先使用后定义?要解决这类问题,你需要使用前向引用。(在预先声明的过程/函数后加forward)

如:

procedure Later (参数列表); forward;

procedure Sooner (参数列表);
begin
  ...
  Later (参数列表);
end;
...
procedure Later;
begin
  ...
  Sooner (参数列表);
end;


示例:

program q;

procedure a;forward;

procedure b;
begin
    writeln('B调取A:');
    a;
end;

procedure a;
begin
    writeln('A过程.');
end;

begin
    b;
end.

相关

维基百科前向声明

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