---
description: "Learn more about: _bstr_t::_bstr_t"
title: "_bstr_t::_bstr_t"
ms.date: 02/02/2021
f1_keywords: ["_bstr_t::_bstr_t"]
helpviewer_keywords: ["BSTR object", "_bstr_t method [C++]", "_bstr_t class"]
---
# `_bstr_t::_bstr_t`

**Microsoft Specific**

Constructs a `_bstr_t` object.

## Syntax

```cpp
_bstr_t( ) throw( );
_bstr_t(
   const _bstr_t& s1
) throw( );
_bstr_t(
   const char* s2
);
_bstr_t(
   const wchar_t* s3
);
_bstr_t(
   const _variant_t& var
);
_bstr_t(
   BSTR bstr,
   bool fCopy
);
```

### Parameters

*`s1`*\
A `_bstr_t` object to be copied.

*`s2`*\
A multibyte string.

*`s3`*\
A Unicode string

*`var`*\
A [_variant_t](../cpp/variant-t-class.md) object.

*`bstr`*\
An existing `BSTR` object.

*`fCopy`*\
If **`false`**, the *`bstr`* argument is attached to the new object without making a copy by calling `SysAllocString`.

## Remarks

The `_bstr_t` class supplies several constructors:

`_bstr_t( )`\
Constructs a default `_bstr_t` object that encapsulates a null `BSTR` object.

`_bstr_t( _bstr_t& s1 )`\
Constructs a `_bstr_t` object as a copy of another. This constructor makes a *shallow* copy, which increments the reference count of the encapsulated `BSTR` object instead of creating a new one.

`_bstr_t( char* s2 )`\
Constructs a `_bstr_t` object by calling `SysAllocString` to create a new `BSTR` object and then encapsulates it. This constructor first performs a multibyte to Unicode conversion.

`_bstr_t( wchar_t* s3 )`\
Constructs a `_bstr_t` object by calling `SysAllocString` to create a new `BSTR` object and then encapsulates it.

`_bstr_t( _variant_t& var )`\
Constructs a `_bstr_t` object from a `_variant_t` object by first retrieving a `BSTR` object from the encapsulated `VARIANT` object.

`_bstr_t( BSTR bstr, bool fCopy )`\
Constructs a `_bstr_t` object from an existing `BSTR` (as opposed to a `wchar_t*` string). If *`fCopy`* is **`false`**, the supplied `BSTR` is attached to the new object without making a new copy by using `SysAllocString`. This constructor is used by wrapper functions in the type library headers to encapsulate and take ownership of a `BSTR` that's returned by an interface method.

**END Microsoft Specific**

## See also

[`_bstr_t` class](../cpp/bstr-t-class.md)\
[`_variant_t` class](../cpp/variant-t-class.md)