VariantChangeType function (oleauto.h)


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.


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


[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


Value Meaning
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.
Converts a VT_BOOL value to a string containing either "True" or "False".
For conversions to or from VT_BSTR, passes LOCALE_NOUSEROVERRIDE to the core coercion routines.
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
The variant type is not a valid type of variant.
The data pointed to by pvarSrc does not fit in the destination type.
The argument could not be coerced to the specified type.
One of the arguments is not valid.
Insufficient memory to complete the operation.


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.


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

See also

Variant Manipulation Functions