TVarData = packed record
case Integer of
0: (VType: TVarType;
case Integer of
0: (Reserved1: Word;
case Integer of
0: (Reserved2, Reserved3: Word;
case Integer of
varSmallInt: (VSmallInt: SmallInt);
varInteger: (VInteger: Integer);
varSingle: (VSingle: Single);
varDouble: (VDouble: Double);
varCurrency: (VCurrency: Currency);
varDate: (VDate: TDateTime);
varOleStr: (VOleStr: PWideChar);
varDispatch: (VDispatch: Pointer);
varError: (VError: HRESULT);
varBoolean: (VBoolean: WordBool);
varUnknown: (VUnknown: Pointer);
varShortInt: (VShortInt: ShortInt);
varByte: (VByte: Byte);
varWord: (VWord: Word);
varLongWord: (VLongWord: LongWord);
varInt64: (VInt64: Int64);
varString: (VString: Pointer);
varAny: (VAny: Pointer);
varArray: (VArray: PVarArray);
varByRef: (VPointer: Pointer);
);
1: (VLongs: array[0..2] of LongInt);
);
2: (VWords: array [0..6] of Word);
3: (VBytes: array [0..13] of Byte);
);
1: (RawData: array [0..3] of LongInt);
end;请问一下里面的Case Integer of 中的Integer是什么东西,整型数?!应当怎么解释!谢 谢
case Integer of
0: (VType: TVarType;
case Integer of
0: (Reserved1: Word;
case Integer of
0: (Reserved2, Reserved3: Word;
case Integer of
varSmallInt: (VSmallInt: SmallInt);
varInteger: (VInteger: Integer);
varSingle: (VSingle: Single);
varDouble: (VDouble: Double);
varCurrency: (VCurrency: Currency);
varDate: (VDate: TDateTime);
varOleStr: (VOleStr: PWideChar);
varDispatch: (VDispatch: Pointer);
varError: (VError: HRESULT);
varBoolean: (VBoolean: WordBool);
varUnknown: (VUnknown: Pointer);
varShortInt: (VShortInt: ShortInt);
varByte: (VByte: Byte);
varWord: (VWord: Word);
varLongWord: (VLongWord: LongWord);
varInt64: (VInt64: Int64);
varString: (VString: Pointer);
varAny: (VAny: Pointer);
varArray: (VArray: PVarArray);
varByRef: (VPointer: Pointer);
);
1: (VLongs: array[0..2] of LongInt);
);
2: (VWords: array [0..6] of Word);
3: (VBytes: array [0..13] of Byte);
);
1: (RawData: array [0..3] of LongInt);
end;请问一下里面的Case Integer of 中的Integer是什么东西,整型数?!应当怎么解释!谢 谢
解决方案 »
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{ and functions (such as True, Integer, or }
{ Writeln) do not have actual declarations.}
{ Instead they are built into the compiler }
{ and are treated as if they were declared }
{ at the beginning of the System unit. 就是说这些东西是看语句是没有意义的(such as True, Integer, or Writeln )
是编译器在编译之前就定义好了的,
再说System是不能通过编译的,
我也不太清楚,以下高手下吧
Instead they are built into the compiler
内置到编译器?
我在查资料,可能是我对RTTI东西有点敏感,
慢慢看,RTTI我有很多理解不了,不求甚解
有没有些书籍讲点这个的
V: Variant;
I: Integer;
S: String;V := I (Integer = varInteger);
v := S (Integer = varString);
I := V (Integer = varInteger);
然后再进行编译
但下面的代码和楼主的变体类型有多少区别啊?
TCMMouseWheel = record
Msg: Cardinal;
ShiftState: TShiftState;
Unused: Byte;
WheelDelta: SmallInt;
case Integer of
0: (
XPos: Smallint;
YPos: Smallint);
1: (
Pos: TSmallPoint;
Result: Longint);
end;
这里的Integer又作何解释,问题见:http://expert.csdn.net/Expert/topic/2453/2453388.xml?temp=.5412561
就多了解了点C,Delphi和C虽然在表现手法上不一样,
但概念多数还是相通的(嘿嘿~~幸好公司有几个VC高手)。
看了C的union,就明白Integer是什么东西了。
Case Integer of
1 : ...
2 : ...
...
在这里Integer和下面的1、2……对应,完全是在源代码级让程序员看起来结构清晰,容易看懂,编译器并不对它处理,也不占相应的内存空间;1、2……后面的变量共用同一快内存空间,具体使用要由程序员自己进行控制。如果采用下面的格式:
Case Tag: Integer of
1 : ...
2 : ...
...
Tag是实实在在的占了一个Integer的内存空间,程序员对内存共享部分进行控制的时候使用Tag会比较方便。
至于变体类型,Delphi没有使用Tag,而是单独定义了 VType域,围绕VType生成了大量控制代码。
VARTYPE vt;
unsigned short wReserved1;
unsigned short wReserved2;
unsigned short wReserved3;
union {
Byte bVal; // VT_UI1.
Short iVal; // VT_I2.
long lVal; // VT_I4.
float fltVal; // VT_R4.
double dblVal; // VT_R8.
VARIANT_BOOL boolVal; // VT_BOOL.
SCODE scode; // VT_ERROR.
CY cyVal; // VT_CY.
DATE date; // VT_DATE.
BSTR bstrVal; // VT_BSTR.
DECIMAL FAR* pdecVal // VT_BYREF|VT_DECIMAL.
IUnknown FAR* punkVal; // VT_UNKNOWN.
IDispatch FAR* pdispVal; // VT_DISPATCH.
SAFEARRAY FAR* parray; // VT_ARRAY|*.
Byte FAR* pbVal; // VT_BYREF|VT_UI1.
short FAR* piVal; // VT_BYREF|VT_I2.
long FAR* plVal; // VT_BYREF|VT_I4.
float FAR* pfltVal; // VT_BYREF|VT_R4.
double FAR* pdblVal; // VT_BYREF|VT_R8.
VARIANT_BOOL FAR* pboolVal; // VT_BYREF|VT_BOOL.
SCODE FAR* pscode; // VT_BYREF|VT_ERROR.
CY FAR* pcyVal; // VT_BYREF|VT_CY.
DATE FAR* pdate; // VT_BYREF|VT_DATE.
BSTR FAR* pbstrVal; // VT_BYREF|VT_BSTR.
IUnknown FAR* FAR* ppunkVal; // VT_BYREF|VT_UNKNOWN.
IDispatch FAR* FAR* ppdispVal; // VT_BYREF|VT_DISPATCH.
SAFEARRAY FAR* FAR* pparray; // VT_ARRAY|*.
VARIANT FAR* pvarVal; // VT_BYREF|VT_VARIANT.
void FAR* byref; // Generic ByRef.
char cVal; // VT_I1.
unsigned short uiVal; // VT_UI2.
unsigned long ulVal; // VT_UI4.
int intVal; // VT_INT.
unsigned int uintVal; // VT_UINT.
char FAR * pcVal; // VT_BYREF|VT_I1.
unsigned short FAR * puiVal; // VT_BYREF|VT_UI2.
unsigned long FAR * pulVal; // VT_BYREF|VT_UI4.
int FAR * pintVal; // VT_BYREF|VT_INT.
unsigned int FAR * puintVal; //VT_BYREF|VT_UINT.
};
};
delphi下面的OleVariant数据类型其实就是windows下面的Variant,一模一样,不信可以打开variants等底层单元瞧瞧源代码:)。你会看到许多的vt
Dephi中定义变体类型的时候,不用Tag而用VType,想必是为了和Windows下的Variant结构统一了
http://expert.csdn.net/Expert/topic/2460/2460034.xml?temp=.9504358