C++Builder代码片断

本文中包含了一些常用的代码片断，看看想想或许有他山之石可以攻玉的可能。

删除别名中所有的表、纯虚函数、虚函数、启动页面、指针、为指针解除引用、表的For循环
变量与常量的声明、检查表是否存在、组件的类名、剪贴板中的文字、字符流、检查表是否已打开
表的状态操作、改变PageControl的标签、向Query传递参数 日期属性 绘制状态条

删除别名中所有的表
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;
}

纯虚函数
//纯虚函数只在基类中出现，而在子类中必须有
//与其匹配的成员函数。程序中申明的子类的实例
//必须为基类中的每一个纯虚函数提供一个重载的成员函数。
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 = ≻
  bc->Display(); // "From Second Derived"
}

虚函数
//虚函数作为其他类的父类的成员函数。
//如果继承子类成员函数中存在与父类成员函数完全相同的函数，
//子类中的成员函数永远有效。
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();


启动页面
USEDATAMODULE("Datamod.cpp", DataModule);
USEFORM("about.cpp", AboutBox);
USEFORM("main.cpp", MainForm);
USEFORM("splash.cpp", SplashForm);
//---------------------------------------------------------------------------
#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;
}


指针
int array[] = { 2, 4, 6, 8, 10}
int myInteger = array[3]; // 值为 8
　
// ----使用指针可以实现同样的功能 -----
int array[] = { 2, 4, 6, 8, 10}
int* myPtr = array;
int myInteger = myPtr[3]; // 值为8


为指针解除引用
int x = 32;
int* ptr = &x;
//解除指针的引用
//以获得内存位置的内容
int y = *ptr; // y = 32


表的For循环
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);
  };
}


变量与常量的声明
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; // * 指针
char* p[20]; // [ ] 数组
void myFunction(int); // ( )函数
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'


检查表是否存在
#include "io.h"
if (access(Table1->TableName.c_str(),0)) //检查表是否存在
{ // 若不存在就创建 ...
  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;


组件的类名
//找出丢失的组件类名
for(int i=0; i < ComponentCount; i++)
{
  if(String(dynamic_cast<TComponent&>(*Components[i]).Name) == "")
  {
    ShowMessage(Components[i]->ClassName());
  }
}


剪贴板中的文字
#include "memory.h" // 包含 auto_ptr<>
#include "clipbrd.hpp" //包含 TClipboard & Clipboard()
// 范例程序，包含了一个memo控件
__fastcall TForm1::TForm1(TComponent* Owner) : TForm(Owner)
{ //创建 TStringList对象
  auto_ptr ClipText(new TStringList); //得到剪贴板中的文字的拷贝
  ClipText->Text = Clipboard()->AsText; //然后加工一下...
  Memo1->Lines->AddStrings(ClipText.get());
}


字符流
//范例一
#include "sstream"
const char *name = "cker";
const char *email = "cker@sina.com";
// 生成 "cker"[SMTP:cker@sina.com]
　
ostringstream ost;
ost << """ << name << ""[SMTP:" << email << "]";
Edit1->Text = ost.str().c_str();
　
//范例二
void TDataModuleEmployee::FullReport(const char *title)
{
  Report.header(title);
  Report << sformat( "Employee #%2d: %s%s", 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();
}


检查表是否已打开
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" "Would 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();
      }
    }
  }
}


表的状态操作
//关闭已打开的表并将他们恢复成初始状态。
void TData::MyTables(TForm * sender)
{
  int i;
  TTable * Table;
  bool *active = new bool[MyClass->ComponentCount];//在动态数组中存放每个表的初始状态，然后关闭所有的表
  for(i = 0; i < MyClass->ComponentCount; i++)
  {
    try
    {
      if((Table = dynamic_cast(MyClass->Components[i])) != NULL)
      {
        active[i] = Table->Active;
        Table->Active = false;
      }
    }
    catch(...) {}; //异常应该只来自于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) //若希望的话，这样允许用户重试！
        {
          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 (...) {}; //异常应该只来自于dynamic cast...
  }
  // 将所有的表设回初始状态。
  for(i = 0; i < MyClass->ComponentCount; i++)
  {
    try
    {
      if((Table = dynamic_cast(MyClass->Components[i])) != NULL)
        Table->Active = active[i];
    }
    catch(...) {};
  }
  delete []active;
}


改变PageControl的标签
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 = "";
      }
    default:
      break;
  }
}


向Query传递参数
// 直接从表向Query传递参数的一种方法
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;


日期属性
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;
  }
}


绘制状态条
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_SINGLELINEDT_CENTER);
      c.Font->Color = clBlack;
      DrawText(c.Handle,Panel->Text.c_str(),-1,(RECT*)&Rect,DT_SINGLELINEDT_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;
    }
  }
}