各位大大: 請問在 delphi 裡如何動態決定變數的資料型態 如 if Fieldtype='Integer' VFieldtYPE:Integer; if Fieldtype='Boolean' VFieldtYPE:Boolean; 是否有辦法做到 Thomas Chiou

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Thomas Chiou

Field type in DB or generic type? For DB, look at TField.DataType.

是 generic type Thomas Chiou

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Thomas Chiou

Hi:    不能 Variant 嗎程式執行時再去做 > -------------------------------- 小弟才疏學淺，若有謬誤請不吝指教 --------------------------------

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Fishman

用 Variant ? 程式執行時再去做 Convert? 抱歉,那程式該如何寫,聽不太懂你的意思

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Thomas Chiou

貼貼help的code參考看看    

    var
  V1, V2, V3, V4, V5: Variant;
  I: Integer;
  D: Double;
  S: string;
begin
  V1 := 1; { integer value }
  V2 := 1234.5678; { real value }
  V3 := 'Hello world!'; { string value }
  V4 := '1000'; { string value }
  V5 := V1   V2   V4; { real value 2235.5678}
  I := V1; { I = 1 (integer value) }
  D := V2; { D = 1234.5678 (real value) }
  S := V3; { S = 'Hello world!' (string value) }
  I := V4; { I = 1000 (integer value) }
  S := V5; { S = '2235.5678' (string value) }    end;    

嗯! 不錯的用法,但這樣會不會有什麼後遺症? 謝謝 Thomas Chiou

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Thomas Chiou

這...可就快問倒我了 可能要看看help或是其他大大幫忙了    在漏漏長的help有看到一句    Variants that contain strings cannot be indexed. That is, if V is a variant that holds a string value, the construction V[1] causes a runtime error. 這應該也是後遺症之一吧!!!!

跟著help慢慢複習,補充一下判斷variant是什麼型態可以用    VarIsNumeric:boolean VarIsFloat:boolean VarIsStr:boolean VarIsOrdinal:boolean    或是殘殘使用    VarIsType(const V: Variant; AVarType: TVarType): Boolean    其中TVarType的值可以是    [繼續轉貼 help]    

    Delphi syntax:    const
  varEmpty    = $0000;
  varNull     = $0001;
  varSmallint = $0002;
  varInteger  = $0003;
  varSingle   = $0004;
  varDouble   = $0005;
  varCurrency = $0006;
  varDate     = $0007;
  varOleStr   = $0008;
  varDispatch = $0009;
  varError    = $000A;
  varBoolean  = $000B;
  varVariant  = $000C;
  varUnknown  = $000D;
  varShortInt = $0010;
  varByte     = $0011;
  varWord     = $0012;
  varLongWord = $0013;
  varInt64    = $0014;
  varStrArg   = $0048;
  varString   = $0100;
  varAny      = $0101; 
  varTypeMask = $0FFF;
  varArray    = $2000;
  varByRef    = $4000;    C   syntax:    static const Shortint varEmpty = 0x0;
static const Shortint varNull = 0x1;
static const Shortint varSmallint = 0x2;
static const Shortint varInteger = 0x3;
static const Shortint varSingle = 0x4;
static const Shortint varDouble = 0x5;
static const Shortint varCurrency = 0x6;
static const Shortint varDate = 0x7;
static const Shortint varOleStr = 0x8;
static const Shortint varDispatch = 0x9;    static const Shortint varError = 0xa;
static const Shortint varBoolean = 0xb;
static const Shortint varVariant = 0xc;
static const Shortint varUnknown = 0xd;
static const Shortint varByte = 0x11;
static const Shortint varStrArg = 0x48;
static const Word varString = 0x100;
static const Word varAny = 0x101;
static const Word varTypeMask = 0xfff;
static const Word varArray = 0x2000;
static const Word varByRef = 0x4000;    

發表人 - hahalin 於 2004/02/02 14:36:01

以前不知在那一本書裡有看到 用 varivant 是為了支援 old automation 而產生的 所以會很耗資源的,不用却也好用,尤其在做一些底層的資料庫介面設計時 謝謝 hahalin Thomas Chiou

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Thomas Chiou

不敢當不敢當 幫忙找找help而已 能幫得上忙才是真的