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

**Microsoft Specific**

A `_bstr_t` object encapsulates the [BSTR data type](/previous-versions/windows/desktop/automat/bstr). The class manages resource allocation and deallocation through function calls to [`SysAllocString`](/windows/win32/api/oleauto/nf-oleauto-sysallocstring) and [`SysFreeString`](/windows/win32/api/oleauto/nf-oleauto-sysfreestring) and other `BSTR` APIs when appropriate. The `_bstr_t` class uses reference counting to avoid excessive overhead.

## Members

### Construction

| Constructor | Description |
|--|--|
| [`_bstr_t`](../cpp/bstr-t-bstr-t.md) | Constructs a `_bstr_t` object. |

### Operations

| Function | Description |
|--|--|
| [`Assign`](../cpp/bstr-t-assign.md) | Copies a `BSTR` into the `BSTR` wrapped by a `_bstr_t`. |
| [`Attach`](../cpp/bstr-t-attach.md) | Links a `_bstr_t` wrapper to a `BSTR`. |
| [`copy`](../cpp/bstr-t-copy.md) | Constructs a copy of the encapsulated `BSTR`. |
| [`Detach`](../cpp/bstr-t-detach.md) | Returns the `BSTR` wrapped by a `_bstr_t` and detaches the `BSTR` from the `_bstr_t`. |
| [`GetAddress`](../cpp/bstr-t-getaddress.md) | Points to the `BSTR` wrapped by a `_bstr_t`. |
| [`GetBSTR`](../cpp/bstr-t-getbstr.md) | Points to the beginning of the `BSTR` wrapped by the `_bstr_t`. |
| [`length`](../cpp/bstr-t-length.md) | Returns the number of characters in the `_bstr_t`. |

### Operators

| Operator | Description |
|--|--|
| [`operator =`](../cpp/bstr-t-operator-equal.md) | Assigns a new value to an existing `_bstr_t` object. |
| [`operator +=`](../cpp/bstr-t-operator-add-equal-plus.md) | Appends characters to the end of the `_bstr_t` object. |
| [`operator +`](../cpp/bstr-t-operator-add-equal-plus.md) | Concatenates two strings. |
| [`operator !`](../cpp/bstr-t-operator-logical-not.md) | Checks if the encapsulated `BSTR` is a NULL string. |
| [`operator ==`](../cpp/bstr-t-relational-operators.md)<br/>[`operator !=`](../cpp/bstr-t-relational-operators.md)<br/>[`operator <`](../cpp/bstr-t-relational-operators.md)<br/>[`operator >`](../cpp/bstr-t-relational-operators.md)<br/>[`operator <=`](../cpp/bstr-t-relational-operators.md)<br/>[`operator >=`](../cpp/bstr-t-relational-operators.md) | Compares two `_bstr_t` objects. |
| [`operator wchar_t*`](../cpp/bstr-t-wchar-t-star-bstr-t-char-star.md)<br/>[`operator char*`](../cpp/bstr-t-wchar-t-star-bstr-t-char-star.md)  | Extract the pointers to the encapsulated Unicode or multibyte `BSTR` object. |

**END Microsoft Specific**

## Requirements

**Header:** \<comutil.h>

**Lib:** *`comsuppw.lib`* or *`comsuppwd.lib`* (For more information, see [`/Zc:wchar_t` (wchar_t is native type)](../build/reference/zc-wchar-t-wchar-t-is-native-type.md))

## See also

[Compiler COM support classes](../cpp/compiler-com-support-classes.md)