OleVariant Variant

OleVariant

ArrayDimCount

 OleVariant;

System.Variants.hpp

 

判断OleVariant 是否为空

System::OleVariant  ov
       if(  !ov.IsNull() )
           procName= ov;

 

 还可以这样

        System::OleVariant ov        
        TValue tv;
        tv=  tv.From<OleVariant>(ov);
Variant po=        tv.AsVariant();
        procName= tv.AsString();
        VarIsNull(v)

VarIsNull(po);

OleVariant 转换字符串

 System::OleVariant ov;

ov.VOleStr;

Variant

VarToStr

 Variant V;
  String mystr;

判断Variant或者字段值是否为null
VarIsNull(v)
VarIsNull(DataSet.FieldByName('fn').Value)
VarIsEmpty

VarToDateTime

  if (TVarData(V).VType == varEmpty)
	ListBox1->Items->Add(L"Variants start મઽૠ૪ empty.");
  VarClear(V);
  TVarData(V).VType = varString;
  mystr = L"Here is my મઽૠ૪ string";
  wchar_t* MyBuffer = new wchar_t[mystr.Length() + 1];
  StrCopy(MyBuffer, mystr.c_str());
  TVarData(V).VString = MyBuffer;
  mystr = (wchar_t *)(TVarData(V).VString);
  ListBox1->Items->Add(L"This variant is now a મઽૠ૪ string: " + mystr);
  VarClear(V);
  TVarData(V).VType = varInteger;
  TVarData(V).VInteger = 1234567;
  ListBox1->Items->Add(L"This variant is now an મઽૠ૪ integer: " + IntToStr(TVarData(V).VInteger));

http://docwiki.embarcadero.com/CodeExamples/XE7/en/SystemVarClear_%28C%2B%2B%29 

fun( const vFileData: OleVariant)
delphi7 里正常  vFileData: OleVariant
delphi10.4.1里 vFileData: OleVariant，提示错误，class EOleSysError with message '类型不匹配
作为函数参数,有以下3种，根据情况定义。导入ocx生成的声明RAD10.4全部是const，D7正常有const有var
function fun1(var vData: OleVariant);

function fun1(const vData: OleVariant);

function fun1(vData: OleVariant);