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VariantChangeType function (oleauto.h)

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Important

This API is affected by the problem described in Microsoft Support topic VarI8FromCy produces incorrect value when CY value is very large.

Converts a variant from one type to another.

Syntax

HRESULT VariantChangeType(
  [out] VARIANTARG       *pvargDest,
  [in]  const VARIANTARG *pvarSrc,
  [in]  USHORT           wFlags,
  [in]  VARTYPE          vt
);

Parameters

[out] pvargDest

The destination variant. If this is the same as pvarSrc, the variant will be converted in place.

[in] pvarSrc

The variant to convert.

[in] wFlags

Flags.

Value Meaning
VARIANT_NOVALUEPROP
 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.
VARIANT_ALPHABOOL
 Converts a VT_BOOL value to a string containing either "True" or "False".
VARIANT_NOUSEROVERRIDE
 For conversions to or from VT_BSTR, passes LOCALE_NOUSEROVERRIDE to the core coercion routines.
VARIANT_LOCALBOOL
 For conversions from VT_BOOL to VT_BSTR and back, uses the language specified by the locale in use on the local computer.

[in] vt

The type to convert to. If the return code is S_OK, the vt field of the *pvargDest is guaranteed to be equal to this value.

Return value

This function can return one of these values.

Return code Description
S_OK
 Success.
DISP_E_BADVARTYPE
 The variant type is not a valid type of variant.
DISP_E_OVERFLOW
 The data pointed to by pvarSrc does not fit in the destination type.
DISP_E_TYPEMISMATCH
 The argument could not be coerced to the specified type.
E_INVALIDARG
One of the arguments is not valid.
E_OUTOFMEMORY
Insufficient memory to complete the operation.

Remarks

The VariantChangeType function handles coercions between the fundamental types (including numeric-to-string and string-to-numeric coercions). The pvarSrc argument is changed during the conversion process. For example, if the source variant is of type VT_BOOL and the destination is of type VT_UINT, the pvarSrc argument is first converted to VT_I2 and then the conversion proceeds. 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 Value property (DISPID_VALUE).

Typically, the implementer of IDispatch::Invoke determines which member is being accessed, and then calls VariantChangeType to get the value of one or more arguments. For example, if the IDispatch call specifies a SetTitle member that takes one string argument, the implementer would call VariantChangeType to attempt to coerce the argument to VT_BSTR. If VariantChangeType does not return an error, the argument could then be obtained directly from the bstrVal field of the VARIANTARG. If VariantChangeType returns DISP_E_TYPEMISMATCH, the implementer would set *puArgErr to 0 (indicating the argument in error) and return DISP_E_TYPEMISMATCH from Invoke.

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

Note  The type of a VARIANTARG should not be changed in the rgvarg array in place.
 

Requirements

Requirement Value
Target Platform Windows
Header oleauto.h
Library OleAut32.lib
DLL OleAut32.dll

See also

Variant Manipulation Functions

VariantChangeTypeEx