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Asked: 2026-05-20T14:29:00+00:00

In Delphi I want to determine whether a particular OleVariant can be cast to

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In Delphi I want to determine whether a particular OleVariant can be cast to a particular data type without raising an exception if it can’t. Exceptions are not for program flow, right?

What I want is something like this, where Type could be anything supported by an OleVariant:

if TryVarAsType(variant, value) then ...

What I don’t want is

try
  value := Type(variant);
  // case where the variant could be converted to a Type
except
  // case where the variant could not be converted to a Type
end;

The case where the variant could not be converted to a Boolean is just a normal case that occurs regularly and doesn’t indicate any kind of error.

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1 Answer

  1. Editorial Team

    you can construct such function using the VariantChangeTypeEx function.

    uses
  VarUtils,
  Variants;

function TryVarAsType( AVariant : OleVariant; const AVarType: TVarType ) :Boolean;
var
   SourceType: TVarType;
begin
  SourceType:=TVarData(AVariant).VType;
  //the types are ole compatible
  if (AVarType and varTypeMask < varInt64) and (SourceType and varTypeMask < varInt64) then
    Result:=
    (SourceType=AVarType) or
    (VariantChangeTypeEx(TVarData(AVariant), TVarData(AVariant), VAR_LOCALE_USER_DEFAULT, 0, AVarType)=VAR_OK)
  else
  Result:=False; //Here you must process the variant pascal types like varString
end;

    and use like this

    TryVarAsType('1',varInteger);
TryVarAsType('s',varInteger)

    this will work with only with ole compatible Variant types 

      varEmpty    = $0000; { vt_empty        0 }
  varNull     = $0001; { vt_null         1 }
  varSmallint = $0002; { vt_i2           2 }
  varInteger  = $0003; { vt_i4           3 }
  varSingle   = $0004; { vt_r4           4 }
  varDouble   = $0005; { vt_r8           5 }
  varCurrency = $0006; { vt_cy           6 }
  varDate     = $0007; { vt_date         7 }
  varOleStr   = $0008; { vt_bstr         8 }
  varDispatch = $0009; { vt_dispatch     9 }
  varError    = $000A; { vt_error       10 }
  varBoolean  = $000B; { vt_bool        11 }
  varVariant  = $000C; { vt_variant     12 }
  varUnknown  = $000D; { vt_unknown     13 }
  varShortInt = $0010; { vt_i1          16 }
  varByte     = $0011; { vt_ui1         17 }
  varWord     = $0012; { vt_ui2         18 }
  varLongWord = $0013; { vt_ui4         19 }
  varInt64    = $0014; { vt_i8          20 }

    for the another types (pascal variants) like varString, varAny you must check the source and destination TVarType and write your own test cases.

    UPDATE

    As @David point me out, the locale settings can produce different results for the same values, so you must consider this answer just as initial step or tip to construct your own function and you must aware of locale settings issues caused in the proposed function.

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