C++Builder常用代碼片斷

C++Builder代碼片斷

本文中包含了一些常用的代碼片斷，看看想想或許有他山之石可以攻玉的可能。 CKER

刪除別名中所有的表	純虛函數	虛函數	啓動頁面	指針
爲指針解除引用	表的For循環	變量與常量的聲明	檢查表是否存在	組件的類名
剪貼板中的文字	字符流	檢查表是否已打開	表的狀態操作	改變PageControl的標籤
向Query傳遞參數	日期屬性	繪製狀態條

　

刪除別名中所有的表
void TData::CleanTemp() 
{ 
  TStringList *myTables = new TStringList();
  TTable *Table = new TTable(this);
  try
  { 
  Session->GetTableNames("Temp", "", True, False, myTables);
  }
  catch (...) {} 
// AnsiString str = myTables->GetText(); 
// ShowMessage(str); 
  for(int count=0; count < myTables->Count; count++) 
  { 
  Table->DatabaseName = "Temp";
  Table->TableName = myTables->Strings[count];
  Table->Close(); 
  Table->DeleteTable(); 
  }
  delete myTables;
  delete Table;
} 
BACK

純虛函數
//純虛函數只在基類中出現，而在子類中必須有
//與其匹配的成員函數。程序中申明的子類的實例
file://必須爲基類中的每一個純虛函數提供一個重載的成員函數。
class TBaseClass 
{ 
  public: 
  virtual void Display() = 0;
};
class TDerivedClass : public TBaseClass 
{ 
  public: 
  void Display() { ShowMessage("From Derived"); }
}; 
　
class TSecondDerivedClass : public TDerivedClass 
{ 
  public: 
  void Display() { ShowMessage("From Second Derived"); } 
}; 
　
void __fastcall TForm1::Button1Click(TObject *Sender) 
{ 
  TDerivedClass dc; dc.Display();// "From Derived" 
  TSecondDerivedClass sc; TBaseClass* bc = &sc; 
  bc->Display(); // "From Second Derived" 
} 
BACK

虛函數
//虛函數作爲其他類的父類的成員函數。
//如果繼承子類成員函數中存在與父類成員函數完全相同的函數，
//子類中的成員函數永遠有效。
class Base 
{
 public: 
  virtual void Display() { ShowMessage("Base Class"); }
};
　
class DerivedOne : public Base 
{ 
  public: 
  void Display() { ShowMessage("DerivedOne"); } 
}; 
　
class DerivedTwo : public Base 
{ 
  public: 
  void Display() { ShowMessage("DerivedTwo"); } 
};
　
Base* pBases[10];
int count = 0;
DerivedOne aDerOne;
DerivedTwo aDerTwo;
pBases[count++] = &aDerOne;
pBases[count++] = &aDerTwo;
for( int i=0; i < count; i++ )
pBases[i]->Display(); 
BACK

啓動頁面
USEDATAMODULE("Datamod.cpp", DataModule);
USEFORM("about.cpp", AboutBox);
USEFORM("main.cpp", MainForm);
USEFORM("splash.cpp", SplashForm);
file://--------------------------------------------------------------------------- 
#include "splash.h"
WINAPI WinMain(HINSTANCE, HINSTANCE, LPSTR, int) 
{
  try 
  { 
  SplashForm = new TSplashForm(Application);
  SplashForm->Show(); 
  SplashForm->Update();
  Application->Initialize();
  Application->Title = "Example of Loading Splash Form"; 
  Application->HelpFile = "SplashHelp.hlp"; 
  Application->CreateForm(__classid(TMainForm), &MainForm); 
  Application->CreateForm(__classid(TDataModule), &DataModule); 
  Application->CreateForm(__classid(TAboutBox), &AboutBox);
  SplashForm->Hide(); 
  SplashForm->Close(); 
  Application->Run(); 
  }
  catch (Exception &exception) 
  { 
  Application->ShowException(&exception);
  }
  return 0;
}
BACK

指針
int array[] = { 2, 4, 6, 8, 10}
int myInteger = array[3]; // 值爲 8
　
// ----使用指針可以實現同樣的功能 ----- 
int array[] = { 2, 4, 6, 8, 10}
int* myPtr = array;
int myInteger = myPtr[3]; // 值爲8 
BACK

爲指針解除引用
int x = 32;
int* ptr = &x; 
//解除指針的引用
file://以獲得內存位置的內容
int y = *ptr; // y = 32 
BACK

表的For循環
void TDataModuleEmployee::ListNames( TStrings *Items )
{
 try
 {
  for ( TableAll->First(); !TableAll->Eof; TableAll->Next() )
  if ( TableAll->FieldByName("Deleted")->AsBoolean == false )
  Items->AddObject( TableAll->FieldByName("Name")->AsString, (TObject *)TableAll->FieldByName("Refnum")->AsInteger );
 }
 catch (Exception &e)
 {
  Application->ShowException(&e);
 }; 
} 
BACK

變量與常量的聲明
char ch;
int count = 1;
char* name = "csdn.net";
struct complex { float my, his;};
float real(complex* p) {return p->my};
const double pi = 3.1415926535897932385;
templetate abc(T a) { return a < 0 ? -a : a; };
enum WebSite { one, two, three, four};
int* a; // * 指針
char* p[20]; // [ ] 數組 
void myFunction(int); // ( )函數 
struct str { short length; char* p; };
char ch1 = 'a'; 
char* p = &ch1; // &引用 ，p保持着ch1的地址 
char ch2 = *p; // ch2 = 'a' 
BACK

檢查表是否存在
#include "io.h" 
if (access(Table1->TableName.c_str(),0)) file://檢查表是否存在 
{ // 若不存在就創建 ... 
 Table1->Active = false;
 Table1->TableType = ttParadox;
 Table1->FieldDefs->Clear();
 Table1->FieldDefs->Add("Myfield", ftString, 15, false);
 Table1->IndexDefs->Clear();
 Table1->CreateTable(); 
 Table1->Active = true;
}
else
 Table1->Active = true; 
BACK

組件的類名
//找出丟失的組件類名
for(int i=0; i < ComponentCount; i++) 
{
 if(String(dynamic_cast<TComponent&>(*Components[i]).Name) == "") 
 { 
  ShowMessage(Components[i]->ClassName());
 }
} 
BACK

剪貼板中的文字
#include "memory.h" // 包含 auto_ptr<> 
#include "clipbrd.hpp" file://包含 TClipboard & Clipboard()
// 範例程序，包含了一個memo控件 
__fastcall TForm1::TForm1(TComponent* Owner) : TForm(Owner)
{ file://創建 TStringList對象 
auto_ptr ClipText(new TStringList); file://得到剪貼板中的文字的拷貝 
ClipText->Text = Clipboard()->AsText; file://然後加工一下... 
Memo1->Lines->AddStrings(ClipText.get()); 
} 
BACK

字符流
//範例一
#include "sstream" 
const char *name = "cker";
const char *email = "[email protected]";
// 生成 "cker"[SMTP:[email protected]] 
　
ostringstream ost;
ost << "/"" << name << "/"[SMTP:" << email << "]";
Edit1->Text = ost.str().c_str();
　
file://範例二
void TDataModuleEmployee::FullReport(const char *title)
{
Report.header(title);
Report << sformat( "Employee #%2d: %s%s/n", TableAllRefnum->Value, TableAllName->Text.c_str(), 
TableAllManagerFlag->Value ?"(Manager)" : "" ) << " Address: " << 
TableAllAddress->Text.c_str() << endl << " " << TableAllCityProvZip->Text.c_str() <<
endl << " " << NameCountry(TableAllCanada->Value) << endl;
Report.footer();
} 
BACK

檢查表是否已打開
void TData::CheckEdit()
{
 for(int i=0; i < ComponentCount; i++)
 { 
  if(dynamic_cast(Components[i]))
  {
   if(((TTable*)Components[i])->State == dsEdit)
   {
    String s = "Table " + Components[i]->Name + " is in edit mode" "/rWould you like to post it before entering new task?";
    if(MessageBox(NULL,s.c_str(),"Table in Edit Mode",MB_YESNO | MB_ICONINFORMATION) == IDYES)
      ((TTable*)Components[i])->Post(); else ((TTable*)Components[i])->Cancel();
   }
  }
 }
} 
BACK

表的狀態操作
//關閉已打開的表並將他們恢復成初始狀態。
void TData::MyTables(TForm * sender)
{
 int i;
 TTable * Table;
 bool *active = new bool[MyClass->ComponentCount];//在動態數組中存放每個表的初始狀態，然後關閉所有的表
 for(i = 0; i < MyClass->ComponentCount; i++)
  {
   try
   {
    if((Table = dynamic_cast(MyClass->Components[i])) != NULL)
     {
      active[i] = Table->Active;
      Table->Active = false;
     }
   }
   catch(...) {}; file://異常應該只來自於dynamic cast...
  }
 for(i = 0; i < MyClass->ComponentCount; i++)
  {
   try
   {
    if((Table = dynamic_cast(MyClass->Components[i])) != NULL)
     { 
      if(Table->DatabaseName != OPTARDatabase->DatabaseName)
        continue;
      DBIResult result = DBIERR_NONE + 1;
      while(result != DBIERR_NONE) file://若希望的話，這樣允許用戶重試！
      {
       result = DbiPackTable (OPTARDatabase->Handle,NULL,Table->TableName.c_str(),NULL, true);
       if(result != DBIERR_NONE)
        { 
         AnsiString rsltText = "Unable to pack " + Table->TableName + "." ;
         char rslt[DBIMAXMSGLEN + 1];
         DbiGetErrorString(result, rslt) rsltText += ". Try again?";
         if(Application->MessageBox(rsltText.c_str(), "Error!",MB_YESNO) != IDYES)
          break; 
        }
      }
     }
   }
   catch (...) {}; file://異常應該只來自於dynamic cast...
  }
 // 將所有的表設回初始狀態。
 for(i = 0; i < MyClass->ComponentCount; i++)
  {
   try
   {
    if((Table = dynamic_cast(MyClass->Components[i])) != NULL) 
     Table->Active = active[i];
   }
   catch(...) {};
  }
 delete []active;
} 
BACK

改變PageControl的標籤
void __fastcall TfmMainForm::Cancel1Click(TObject *Sender)
{
 int i;
 switch (PageControl1->ActivePage->Tag))
  {
   case 1:
     for (i=0; i < ComponentCount; i++)
      {
       if (dynamic_cast(Components[i]))
         dynamic_cast(Components[i])->Enabled = false;
      }
     Data->tbDetail->Cancel();
     break;
   case 2:
     for (i=0; i < ComponentCount; i++)
      {
       if (dynamic_cast(Components[i]))
         dynamic_cast(Components[i])->Enabled = false;
      }
      Data->tbDetail->Cancel();
      break;
   case 3:
     for (i=0; i < ComponentCount; i++)
      {
       if (dynamic_cast(Components[i]))
         dynamic_cast(Components[i])->Text = "";
      }
      break;
  }
} 
BACK

向Query傳遞參數
// 直接從表向Query傳遞參數的一種方法
TQuery *Query = new TQuery(this);
Query->DatabaseName = "dbServer";
Query->SQL->Clear();
Query->SQL->Add("DELETE FROM 'Events.DB' WHERE (TicketNo = " + Data->tbProblem->FieldByName("TicketNo")->AsString + ")" );
Query->ExecSQL();
Query->Close();
delete Query; 
BACK

日期屬性
TMaskEdit *meOpen;
TLabel *lbCount1;
TDateTime Date2;
void __fastcall TfmMainForm::CountOpen(TObject *Sender)
{
 switch(dynamic_cast<TComponent&>(*Sender).Tag)
  {
   case 1:
    count1 = StrToInt(lbCount1->Caption);
    count1 += 1;
    Date2 = Now() + count1;
    meOpen->Text = Date2.DateString();
    lbCount1->Caption = IntToStr(count1);
    break;
   case 2:
    count1 = StrToInt(lbCount1->Caption);
    count1 -= 1;
    Date2 = Now() + count1;
    meOpen->Text = Date2.DateString();
    lbCount1->Caption = IntToStr(count1);
    break;
  }
} 
BACK

繪製狀態條
void __fastcall TForm1::StatusBar1DrawPanel(TStatusBar *StatusBar, TStatusPanel *Panel, const TRect &Rect)
{
 TCanvas& c = *StatusBar->Canvas;
 switch (Panel->Index)
  {
   case 0 :
     {
      StatusBar1->Panels->Items[0]->Text = "Hello C++";
      c.Brush->Style = bsClear;
      TRect temp = Rect;
      temp.Top += 1;
      temp.Left += 1; 
      c.Font->Color = clWhite;
      DrawText(c.Handle, Panel->Text.c_str(), -1,(RECT*)&temp, DT_SINGLELINE | DT_CENTER);
      c.Font->Color = clBlack;
      DrawText(c.Handle, Panel->Text.c_str(), -1, (RECT*)&Rect, DT_SINGLELINE | DT_CENTER);
      break;
     }
   case 1:
     {
      c.Brush->Color = clYellow;
      c.FillRect(Rect);
      c.Font->Color = clRed;
      DrawText(c.Handle,"clYellow Color", -1, (RECT*)&Rect, DT_SINGLELINE | DT_CENTER);
      break;
     }
   case 2:
     {
      Graphics::TBitmap* bm = new Graphics::TBitmap;
      bm->Handle = LoadBitmap(NULL, MAKEINTRESOURCE(32760));
      c.Draw(Rect.Left, Rect.Top, bm);
      delete bm;
      break;
     }
  }
}
 BACK