Delphi的Format函数大家都用得很多,第二个参数用着确实很方便。最近在数据库开发应用中需要自己创建一个带array of const参数的函数,对于常用的类型String,Integer,Pointer处理都没什么问题,但当用到Widestring类型时却出错,摸索了一上午,感觉获益良多。现在将问题、解决问题的思路、分析方法等一一道来,希望对诸君有所启发就达到了我写这篇文章的目的了!
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
///环境:Winxp + D7
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
///进入D7,在默认的新建工程中增加一过程Test(m: Array of const);
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
procedure TForm1.test(m: array of const);
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
var
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
i, zero: Integer;
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
s, t: String;
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
c: Char;
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
const
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
sBoolean: Array [Boolean] of string = ('False', 'True');
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
begin
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
s := '';
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
for i := 0 to High(m) do with m[i] do
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
case VType of //写到这,按住Ctrl点击VType,打开System单元,将VType的枚举值贴到Case语句
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
vtInteger: (VInteger: Integer; VType: Byte);
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
vtBoolean: (VBoolean: Boolean);
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
vtChar: (VChar: Char);
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
vtExtended: (VExtended: PExtended);
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
vtString: (VString: PShortString);
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
vtPointer: (VPointer: Pointer);
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
vtPChar: (VPChar: PChar);
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
vtObject: (VObject: TObject);
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
vtClass: (VClass: TClass);
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
vtWideChar: (VWideChar: WideChar);
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
vtPWideChar: (VPWideChar: PWideChar);
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
vtAnsiString: (VAnsiString: Pointer);
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
vtCurrency: (VCurrency: PCurrency);
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
vtVariant: (VVariant: PVariant);
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
vtInterface: (VInterface: Pointer);
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
vtWideString: (VWideString: Pointer);
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
vtInt64: (VInt64: PInt64);
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
end;
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
Delete(s, 1, 1);
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
Self.Caption := s;
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
end;
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
///继续写,对各枚举值进行处理!这里作一下解释,Array of const正是由TVarRec类型组成的!
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
///请看Case of语句中的代码:
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
vtInteger: s := s + ';' + IntToStr(VInteger);
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
vtBoolean: s := s + ';' + sBoolean[VBoolean];
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
vtChar: s := s + ';' + VChar;
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
vtExtended: s := s + ';' + FloatToStr(VExtended^);
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
vtString:
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
if Assigned(VString) then begin
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
t := VString^;
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
s := s + ';' + t;
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
end;
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
vtPointer:
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
if Assigned(VPointer) then
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
s := Format('%S; Pointer: $%X ',[s, Integer(VPointer)]);
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
vtPChar:
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
if Assigned(VPChar) then begin
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
t := VPChar^;
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
s := s + ';' + t;
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
end;
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
vtObject:
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
if Assigned(VObject) then
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
s := Format('%S; $%X ClassName: %S ',[s, Integer(@VObject), VObject.ClassName]);
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
vtClass:
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
if Assigned(VClass) then
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
s := Format('%S; Class Reference $%X - ClassName: %S ',[s, Integer(VClass), VClass.ClassName]);
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
vtWideChar:
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
begin
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
t := VWideChar;
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
s := s + ';' + t;
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
end;
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
vtPWideChar:
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
if Assigned(VPWideChar) then begin
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
t := VPWideChar^;
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
s := s + ';' + t;
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
end;
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
vtAnsiString:
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
if Assigned(VAnsiString) then begin
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
t := PChar(VAnsiString);
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
s := s + ';' + t;
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
end;
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
vtCurrency:
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
if Assigned(VCurrency) then
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
s := s + ';' + FloatToStr(VCurrency^);
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
vtVariant:
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
if Assigned(VVariant) then
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
s := s + '; This is variant ';
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
vtInterface:
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
if Assigned(VInterface) then
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
s := Format('%S; Interface: $%X',[s, Integer(VInterface)]);
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
vtWideString:
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
if Assigned(VWideString) then begin
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
t := PWideString(VWideString)^;
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
s := s + ';' + t;
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
end;
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
vtInt64:
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
if Assigned(VInt64) then
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
s := s + ';' + IntToStr(VInt64^);
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
加上一按钮测试该函数
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
procedure TForm1.Button1Click(Sender: TObject);
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
var
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
ws: WideString;
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
begin
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
ws := 'dda这是一个测试dfa';
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
test([self, 'sdf', 2.3324, ws, TForm]);
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
end;
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
可以看到测试结果,变量ws的值没有显示出来,怎么办呢?
我们可以看到WideString类型的值是指针,我们就从这里着手,在事件中添加一句:
Button1.Caption := Format('$%X',[Integer(@ws)]);
此句的作用是显示出ws的地址
再在Test函数中也加上类似的语句,并注释掉无用的语句:
//t := PWideString(VWideString)^;
//s := s + ';' + t;
s := s + ';' + Format('$%X',[Integer(VWideString)]);
运行可看到二个地址不一样,说明Delphi对传入的参数数据作了复制
因此将其强制转换成PWidechar应该可以,增加一变量声明
w: WideString;
w := PWideString(VWideString)^;
s := s + ';' + w;
但运行结果却只显示一个字符,别沮丧,已经摸到门道了!
我们知道Format可以处理Widestring类型,这里只得到一个字符,说明字符被截断了。Delphi中的字符串是以#0结束,Widestring以二个#0结束,可以肯定w := PWideString(VWideString)^这句Delphi作转换时肯定将其默认作为AnsiString处理了。分析到这里已经可动手写下去了.....
p: PByte;
if Assigned(VWideString) then begin
t := '';
zero := 0;
p := VWideString;
repeat
c := char(p^);
inc(p);
if c = #0 then
inc(zero) else
begin
zero := 0;
t := t + c;
end;
until zero = 2;
s := s + ';' + t;
end;
但是显示汉字却变成乱码了,而且处理也显得臃肿。到这里我们已经明白了,VWideString所指示的字符串是二字节宽字符串,而且Intel的字节顺序也是低位在前,高位在后。因此可用PWord进行处理!
删除c,zero,w变量,p改成:
p: PWord;
if Assigned(VWideString) then begin
t := '';
p := VWideString;
repeat
t := t + widechar(p^);
inc(p);
until p^ = 0;
s := s + ';' + t;
end;
可以看到核心代码已经很精练了,运行已经显示正常,汉字也无乱码了!至此我们似乎是大功告成了,但静下来想想,Delphi支持WideString到String的转换,它也应该有这样的处理代码。
而且在循环中t := t + widechar(p^);语句处下一断点,运行到断点处,再打开CPU窗口,看到看似简洁的代码,单此一句,编译器都要给它加上一大堆处理代码。找到系统的字符串处理函数很有必要,经过在System.pas单元中搜索WideString,找到函数:procedure WideCharToStrVar(Source: PWideChar; var Dest: string);
呵呵,这正是我们要的!!!
现在循环语句及P变量都可删除了,代码我就省略了。
http://www.cnblogs.com/sonicit/archive/2008/03/23/1118524.html