Question

您好我在这里学到了很多关于使用函数的知识。我学到的很多东西都是： - - 来自另一个表单的函数返回值 - 来自另一个无形单元的函数返回值

这一次，我希望函数能够从无形单元 THROUGH 获得另一种形式的引用。

使用上面的这些方法，我尝试让函数从无形单元 THROUGH 返回另一种形式。似乎我无法让它正常工作。

Unit1.h

//---------------------------------------------------------------------------
#ifndef Unit1H
#define Unit1H
//---------------------------------------------------------------------------
#include <System.Classes.hpp>
#include <Vcl.Controls.hpp>
#include <Vcl.StdCtrls.hpp>
#include <Vcl.Forms.hpp>
//---------------------------------------------------------------------------
class TForm1 : public TForm
{
__published:    // IDE-managed Components
TButton *Button3;
TLabel *Label3;
void __fastcall Button3Click(TObject *Sender);
private:    // User declarations
public:     // User declarations
__fastcall TForm1(TComponent* Owner);
};
//---------------------------------------------------------------------------
extern PACKAGE TForm1 *Form1;
//---------------------------------------------------------------------------
#endif

Unit1.cpp

//---------------------------------------------------------------------------

#include <vcl.h>
#pragma hdrstop

#include "Unit1.h"
#include "Unit2.h"

//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
TForm1 *Form1;

extern String getQuote();

String quote1;


//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
: TForm(Owner)
{
}

//---------------------------------------------------------------------------
void __fastcall TForm1::Button3Click(TObject *Sender)
{
quote1 = Form2->getQuote();
Label3->Caption = quote1;
}
//---------------------------------------------------------------------------

Unit2.h

//---------------------------------------------------------------------------

#ifndef Unit2H
#define Unit2H
//---------------------------------------------------------------------------
#include <System.Classes.hpp>
#include <Vcl.Controls.hpp>
#include <Vcl.StdCtrls.hpp>
#include <Vcl.Forms.hpp>

extern String FindQuote();

//---------------------------------------------------------------------------
class TForm2 : public TForm
{
__published:    // IDE-managed Components
private:    // User declarations
public:     // User declarations
__fastcall TForm2(TComponent* Owner);

String getQuote();
};
//---------------------------------------------------------------------------
extern PACKAGE TForm2 *Form2;
//---------------------------------------------------------------------------
#endif

Unit2.cpp

//---------------------------------------------------------------------------
#include <vcl.h>
#pragma hdrstop

#include "Unit2.h"
#include "Unit3.h"

extern String FindQuote();

//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
TForm2 *Form2;

//---------------------------------------------------------------------------
__fastcall TForm2::TForm2(TComponent* Owner)
: TForm(Owner)
{
}
//---------------------------------------------------------------------------

String TForm2::getQuote()
{
    return FindQuote();
}

//---------------------------------------------------------------------------

Unit3.h

//---------------------------------------------------------------------------

#ifndef Unit3H
#define Unit3H

//---------------------------------------------------------------------------

// declare the function here in the header file.

String FindQuote();

#endif

Unit3.cpp

//---------------------------------------------------------------------------

#pragma hdrstop

#include "Unit3.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)

String FindQuote()
{
    return "He with whom neither slander that gradually soaks into the mind, nor statements that startle like a wound in the flesh, are successful may be called intelligent indeed.";
}

我收到了错误“

[bcc32 Error] Unit3.h(11): E2141 Declaration syntax error
  Full parser context
Unit3.cpp(5): #include Unit3.h
[bcc32 Error] Unit3.cpp(14): E2238 Multiple declaration for 'String'
[bcc32 Error] Unit3.h(11): E2344 Earlier declaration of 'String'
[bcc32 Error] Unit3.cpp(14): E2141 Declaration syntax error

“。如何解决？

Answer 1

Unit1.cpp不应该有extern String getQuote();。无论如何，该名称没有自由功能，你永远不会打电话给它。

Unit2.h和Unit2.cpp都不应该extern String FindQuote();。相反，Unit2.cpp应#include "Unit3.h"（它确实如此），以便它看到String FindQuote();。

如果您不知道，extern是多余的，extern X f();与X f();相同。

您的错误是String尚未声明。在使用#include <vcl.h>的任何代码之前，您必须看到String。您可以将其放在Unit3.h的顶部，也可以将其放在Unit3.cpp #pragma hdrstop之前。

您应该在刚刚显示的消息之前收到其他错误/警告消息，提醒您String未声明。在解决后来的问题之前，请始终先解决您收到的第一个错误/警告，因为它们可能是从第一个错误中级联出来的虚假消息。

函数从无形单元到表单元的返回值

1 个答案: