---
name: "std::locale_id"
section: "3"
platform: "linux"
package: "gcc"
version: "16.2.1+r23+gd564253eb6c8-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/std::locale_id"
---

# std::locale\_id(3)

Facet ID class.

## NAME

std::locale::id - Facet ID class.

## SYNOPSIS

\#include \<locale\>

### Public Member Functions

**id** ()\
 Constructor.  size\_t **\_M\_id** () const  throw ()\

### Friends

template\<typename \_Facet\> const \_Facet \* **\_\_try\_use\_facet** (const locale &\_\_loc)\
 template\<typename \_Facet\> bool **has\_facet** (const locale &\_\_loc)  throw ()\
 Test for the presence of a facet.  class **locale**\
 class **locale::\_Impl**\
 template\<typename \_Facet\> const \_Facet & **use\_facet** (const locale &\_\_loc)\
 Return a facet.

## Detailed Description

Facet ID class.

The ID class provides facets with an index used to identify them. Every facet class must define a public static member locale::id, or be derived from a facet that provides this member, otherwise the facet cannot be used in a locale. The locale::id ensures that each class type gets a unique identifier.

## Constructor & Destructor Documentation

### std::locale::id::id () \[inline\]

Constructor.

## Friends And Related Symbol Documentation

### template\<typename \_Facet\> bool has\_facet (const locale & \_\_loc) \[friend\]

Test for the presence of a facet. has\_facet tests the locale argument for the presence of the facet type provided as the template parameter. Facets derived from the facet parameter will also return true.

**Template Parameters**

*\_Facet* The facet type to test the presence of.

**Parameters**

*\_\_loc* The locale to test.

**Returns**

true if \_\_loc contains a facet of type \_Facet, else false.

### template\<typename \_Facet\> const \_Facet & use\_facet (const locale & \_\_loc) \[friend\]

Return a facet. use\_facet looks for and returns a reference to a facet of type Facet where Facet is the template parameter. If has\_facet(locale) is true, there is a suitable facet to return. It throws std::bad\_cast if the locale doesn't contain a facet of type Facet.

**Template Parameters**

*\_Facet* The facet type to access.

**Parameters**

*\_\_loc* The locale to use.

**Returns**

Reference to facet of type Facet.

**Exceptions**

**std::bad\_cast if** \_\_loc **doesn't contain a facet of type \_Facet.**

## Author

**Generated automatically by Doxygen for libstdc++ from the source code.**