如何解决编译 C++Builder 6 项目时出现“未解决的外部”错误
我在编译 C++Builder 6 线程项目时遇到一些错误。我不知道如何修复它们。
Unit1.cpp:
//---------------------------------------------------------------------------
#include <vcl.h>
#pragma hdrstop
#include "Unit1.h"
using namespace std;
int i1 = 0,i2 = 0;
T1 *Thread1,*Thread2;
bool Term1,Term2;
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
TForm1 *Form1;
//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
: TForm(Owner)
{
}
void __fastcall T1::Execute()
{
do
Synchronize (UpdateTimer);
while (!Terminated);
}
//-----------------------------------------------
void __fastcall T1::UpdateTimer()
{
Timer->Enabled = !Terminated;
}
//---------------------------------------------------------------------------
void __fastcall TForm1::FormCreate(TObject *Sender)
{
ComboBox1->ItemIndex = 3;
ComboBox2->ItemIndex = 3;
Thread1 = new T1(false);
Thread1->Timer = Timer1;
Thread1->FreeOnTerminate = true;
Term1 = false;
Thread2 = new T1(true);
Thread2->Timer = Timer2;
Thread2->FreeOnTerminate = true;
Term2 = false;
}
//---------------------------------------------------------------------------
void __fastcall TForm1::Timer1Timer(TObject *Sender)
{
i1++;
Label1->Caption = i1;
Timer1->Enabled = false;
}
//---------------------------------------------------------------------------
void __fastcall TForm1::Timer2Timer(TObject *Sender)
{
i2++;
Label2->Caption = i2;
Timer2->Enabled = false;
}
//---------------------------------------------------------------------------
void __fastcall TForm1::BRes1Click(TObject *Sender)
{
if (!Term1)
Thread1->Resume();
else ShowMessage("Ïîòîê óæå çàâåðøåí");
}
//---------------------------------------------------------------------------
void __fastcall TForm1::BRes2Click(TObject *Sender)
{
if (!Term2)
Thread2->Resume();
else ShowMessage("Ïîòîê óæå çàâåðøåí");
}
//---------------------------------------------------------------------------
void __fastcall TForm1::BTerm1Click(TObject *Sender)
{
Thread1->Terminate();
Term1 = true;
}
//---------------------------------------------------------------------------
void __fastcall TForm1::BTerm2Click(TObject *Sender)
{
Thread2->Terminate();
Term2 = true;
}
//---------------------------------------------------------------------------
void __fastcall TForm1::BSuspend1Click(TObject *Sender)
{
if (!Term1)
Thread1->Suspend();
else ShowMessage("Ïîòîê óæå çàâåðøåí");
}
//---------------------------------------------------------------------------
void __fastcall TForm1::BSuspend2Click(TObject *Sender)
{
if (!Term2)
Thread2->Suspend();
else ShowMessage("Ïîòîê óæå çàâåðøåí");
}
//---------------------------------------------------------------------------
void __fastcall TForm1::BSyncclick(TObject *Sender)
{
if (Term1 || Term2)
ShowMessage("Ïîòîê óæå çàâåðøåí");
else
{
if (!Thread1->Suspended)
Thread1->Suspend();
if (!Thread2->Suspended)
Thread2->Suspend();
Timer1->Enabled = false;
Timer2->Enabled = false;
i1 = 0;
i2 = 0;
Thread1->Resume();
Thread2->Resume();
}
}
//---------------------------------------------------------------------------
void __fastcall TForm1::ComboBox1Change(TObject *Sender)
{
if (Term1)
ShowMessage("Ïîòîê óæå çàâåðøåí");
else
switch (ComboBox1->ItemIndex)
{
case 0: Thread1->Priority = tpIdle; break;
case 1: Thread1->Priority = tpLowest; break;
case 2: Thread1->Priority = tpLower; break;
case 3: Thread1->Priority = tpnormal; break;
case 4: Thread1->Priority = tpHigher; break;
case 5: Thread1->Priority = tpHighest; break;
case 6: Thread1->Priority = tpTimeCritical; break;
}
}
//---------------------------------------------------------------------------
void __fastcall TForm1::ComboBox2Change(TObject *Sender)
{
if (Term2)
ShowMessage("Ïîòîê óæå çàâåðøåí");
else
switch (ComboBox2->ItemIndex)
{
case 0: Thread2->Priority = tpIdle; break;
case 1: Thread2->Priority = tpLowest; break;
case 2: Thread2->Priority = tpLower; break;
case 3: Thread2->Priority = tpnormal; break;
case 4: Thread2->Priority = tpHigher; break;
case 5: Thread2->Priority = tpHighest; break;
case 6: Thread2->Priority = tpTimeCritical; break;
}
}
//---------------------------------------------------------------------------
Uni1.h
//---------------------------------------------------------------------------
#ifndef Unit1H
#define Unit1H
//---------------------------------------------------------------------------
#include <Classes.hpp>
#include <Controls.hpp>
#include <StdCtrls.hpp>
#include <Forms.hpp>
#include <ExtCtrls.hpp>
//---------------------------------------------------------------------------
class TForm1 : public TForm
{
__published: // IDE-managed Components
TGroupBox *GroupBox1;
TGroupBox *GroupBox2;
TLabel *Label1;
TButton *BRes1;
TButton *BSuspend1;
TButton *BTerm1;
TLabel *Label2;
TButton *BRes2;
TButton *BSuspend2;
TButton *BTerm2;
TComboBox *ComboBox1;
TComboBox *ComboBox2;
TButton *BSync;
TTimer *Timer1;
TTimer *Timer2;
void __fastcall FormCreate(TObject *Sender);
void __fastcall Timer1Timer(TObject *Sender);
void __fastcall Timer2Timer(TObject *Sender);
void __fastcall BRes1Click(TObject *Sender);
void __fastcall BRes2Click(TObject *Sender);
void __fastcall BTerm1Click(TObject *Sender);
void __fastcall BTerm2Click(TObject *Sender);
void __fastcall BSuspend1Click(TObject *Sender);
void __fastcall BSuspend2Click(TObject *Sender);
void __fastcall BSyncclick(TObject *Sender);
void __fastcall ComboBox1Change(TObject *Sender);
void __fastcall ComboBox2Change(TObject *Sender);
private: // User declarations
public: // User declarations
__fastcall TForm1(TComponent* Owner);
};
class T1 : public TThread
{
private:
void _fastcall UpdateTimer();
protected:
void _fastcall Execute();
public:
__fastcall T1(bool CreateSuspended);
TTimer *Timer;
};
//---------------------------------------------------------------------------
extern PACKAGE TForm1 *Form1;
//---------------------------------------------------------------------------
#endif
错误:
[Linker Error] Unresolved external 't1::' referenced from C:\USERS\ALEXEY\DESKTOP\CCC\UNIT1.OBJ
[Linker Error] Unresolved external '__fastcall T1::T1(bool)' referenced from C:\USERS\ALEXEY\DESKTOP\CCC\UNIT1.OBJ
解决方法
您已经声明了一个类 T1
,其中声明了一个构造函数,但您实际上并没有实现该构造函数。这就是链接器所抱怨的。
您需要将该实现添加到您的 .cpp
文件中,例如:
__fastcall T1::T1(bool CreateSuspended)
: TThread(CreateSuspended)
{
FreeOnTerminate = true; // <-- this should be moved in here
}
这将解决链接器错误。
话虽如此,您的代码存在一些设计缺陷。
您正在使用 Thread1
创建 CreateSuspended=false
对象,这允许它在构造函数完成后立即开始运行。但是在构造函数退出之前,您不会分配其 Timer
成员。因此线程可以在分配 Timer
之前开始运行。这在您的示例中“有效”的唯一原因是您使用 TThread::Synchronize()
直到 T1::UpdateTimer()
1 分配了 {{1} } 成员并退出
1:顺便说一句,您根本不应该在 C++ 中使用该事件,因为它会导致未定义行为。改用 Form 的构造函数。
但这不是一个值得依赖的好设计。由于您的线程类依赖于外部 TForm1::FormCreate()
对象,您应该:
-
用
Timer
创建TTimer
对象,然后在完全初始化其成员后Thread1
该线程。这就是您对CreateSuspended=true
对象所做的。 -
将所需的
Resume()
对象指针传递给每个线程的构造函数,例如:
Thread2
此外,您为两个线程都设置了 TTimer
,但是您没有为每个线程分配一个 class T1 : public TThread
{
private:
TTimer *Timer;
void _fastcall UpdateTimer();
protected:
void _fastcall Execute();
public:
__fastcall T1(bool CreateSuspended,TTimer *ATimer);
};
...
__fastcall T1::T1(bool CreateSuspended,TTimer *ATimer)
: TThread(CreateSuspended),Timer(ATimer)
{
FreeOnTerminate = true;
}
...
Thread1 = new T1(false,Timer1);
Thread2 = new T1(true,Timer2);
事件处理程序,因此您无法确定线程在何时真正有效您尝试在按钮 FreeOnTerminate=true
事件处理程序中访问它们。如果线程因任何原因终止,包括意外崩溃,那么您将访问悬空指针。
此外,您不应出于任何原因从该线程自己的 OnTerminate
方法之外OnClick
运行正在运行的线程。您不知道暂停时线程的状态。它可能(在这种情况下很可能会)在 Suspend()
调用的中间,这可能导致等待挂起的 Execute()
完成其工作的死锁。如果您想暂停工作线程,请改用单独的标志,甚至是 Synchronize()
,线程可以在安全且适当的情况下定期检查该标志。
最后,在工作线程的紧密循环中调用 Synchronize()
,正如您所做的那样,是对工作线程的完全浪费,因为 ALL它的大部分工作仅在主 UI 线程中执行。你也可以完全摆脱你的 TEvent
类。使用 TThread::Synchronize()
或 TThread
循环、TTimer
事件处理程序或 PostMessage()
事件处理程序等就足够了。有许多不同的方法来解决这个问题。
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