VariantChangeType

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

Converts a variant from one type to another.

Parameters

pvargDest
Pointer to the VARIANTARG to receive the coerced type. If this is the same as pvarSrc, the variant will be converted in place.
pvarSrc
Pointer to the source VARIANTARG to be coerced.
wFlags
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
The type to coerce to. If the return code is S_OK, the vt field of the *pvargDest is always the same as this value.

Return Value

The return value obtained from the returned HRESULT is one of the following.

Return value Meaning
S_OK Success.
DISP_E_BADVARTYPE The variant type vt 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 invalid.
E_OUTOFMEMORY Memory could not be allocated for the conversion.

Comments

The VariantChangeType function 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 Value property (DISPID_VALUE).

Typically, the implementor 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 implementor 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 implementor would set *puArgErr to 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.

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

QuickInfo

  Windows NT: Use version 3.1 and later.
  Windows: Use Windows 95 and later.
  Header: Declared in oleauto.h.
  Import Library: Link with oleaut32.lib.

See Also

VariantChangeTypeEx