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4/8/2010

This function converts a variant from one type to another.

Syntax 

HRESULT VariantChangeType( 
  VARIANTARG FAR* 
pvargDest, 
  VARIANTARG FAR* 
pvarSrc, 
  unsigned short 
wFlags, 
  VARTYPE 
vt 
);

Parameters

pvargDest

[out] Pointer to the VarBoolFromDispto receive the coerced type. If this is the same as pvarSrc, the variant is converted in place.

pvarSrc

[in] Pointer to the source VARIANTARGto be coerced.

wFlags

[in] Flags that control the coercion.

The only defined flag is VARIANT_NOVALUEPROP, which prevents the function from attempting to coerce an object to a fundamental type by getting the Value property.

Applications should set this flag only if necessary, because it makes their behavior inconsistent with other applications.

vt

[in] Specifies the type to coerce to. If the return code is S_OK, the vtmember of the VARIANTARGspecified by * pvargDestis the same as this value.

Return Value

Returns the HRESULT values shown in the following table.

Value Description

S_OK

Success.

DISP_E_BADVARTYPE

The variant type vtis not a valid type of variant.

DISP_E_OVERFLOW

The data pointed to by pvarSrcdoes not fit in the destination type.

DISP_E_TYPEMISMATCH

The argument could not be coerced to the specified type.

E_INVALIDARG

An argument is invalid.

E_OUTOFMEMORY

Memory could not be allocated for the conversion.

Remarks

Passing invalid (and under some circumstances NULL) pointers to this function causes an unexpected termination of the application.

The VariantChangeTypefunction handles coercions between the fundamental types (including numeric-to-string and string-to-numeric coercions).

A variant that has VT_BYREF set is coerced to a value by obtaining the referenced value. An object is coerced to a value by invoking the object's Valueproperty (DISPID_VALUE).

Typically, the implementer of IDispatch::Invokedetermines which member is being accessed and then calls VariantChangeTypeto get the value of one or more arguments.

For example, if the IDispatchcall specifies a SetTitlemember that takes one string argument, the implementer would call VariantChangeTypeto attempt to coerce the argument to VT_BSTR.

If VariantChangeTypedoes not return an error, the argument could then be obtained directly from the bstrValmember of the VARIANTARG.

If VariantChangeTypereturns DISP_E_TYPEMISMATCH, the implementor would set * puArgErrto 0 (indicating the argument in error) and return DISP_E_TYPEMISMATCH from IDispatch::Invoke.

Arrays of one type cannot be converted to arrays of another type with this function.

The type of a VARIANTARG should not be changed in the rgvargarray in place.

Requirements

Header oleauto.h
Library oleaut32.lib
Windows Embedded CE Windows CE 2.0 and later
Windows Mobile Windows Mobile Version 5.0 and later

See Also