---
name: "std::error_category"
section: "3cxx"
platform: "linux"
package: "libstdc++-12-doc"
version: "12.4.0-5"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/std::error_category/3cxx"
---

# std::error\_category(3cxx)

## NAME

std::error\_category

## SYNOPSIS

`#include <system_error>`

### Public Member Functions

**error\_category** (const **error\_category** &)=**delete**\
 **virtual** **error\_condition** **default\_error\_condition** (int \_\_i) const noexcept\
 Return an error\_condition corresponding to `i` in this category.  **virtual** bool **equivalent** (const **error\_code** &**\_\_code**, int \_\_i) const noexcept\
 Test whether `code` corresponds to `i` for this category.  **virtual** bool **equivalent** (int \_\_i, const **error\_condition** &**\_\_cond**) const noexcept\
 Test whether `cond` corresponds to `i` for this category.  **virtual** **string** **message** (int) const =0\
 **virtual** const char \* **name** () const noexcept=0\
 A string that identifies the error category.  bool **operator!=** (const **error\_category** &\_\_other) const noexcept\
 bool **operator\<** (const **error\_category** &\_\_other) const noexcept\
 Ordered comparison that defines a total order for error categories.  **error\_category** & **operator=** (const **error\_category** &)=**delete**\
 bool **operator==** (const **error\_category** &\_\_other) const noexcept\
 An error\_category only compares equal to itself.

## Detailed Description

Abstract base class for types defining a category of error codes.

An error category defines a context that gives meaning to the integer stored in an `error_code` or `error_condition` object. For example, the standard `errno` constants such a `EINVAL` and `ENOMEM` are associated with the 'generic' category and other OS-specific error numbers are associated with the 'system' category, but a user-defined category might give different meanings to the same numerical values.

A user-defined category can override the `equivalent` member functions to define correspondence between errors in different categories. For example, a category for errors from disk I/O could consider some of its error numbers equivalent to ENOSPC and ENOENT in the generic category.

**Since**

C++11

## Member Function Documentation

### virtual error\_condition std::error\_category::default\_error\_condition (int \_\_i) const` [virtual]`, ` [noexcept]`

Return an error\_condition corresponding to `i` in this category.

### virtual bool std::error\_category::equivalent (const error\_code & \_\_code, int \_\_i) const` [virtual]`, ` [noexcept]`

Test whether `code` corresponds to `i` for this category.

### virtual bool std::error\_category::equivalent (int \_\_i, const error\_condition & \_\_cond) const` [virtual]`, ` [noexcept]`

Test whether `cond` corresponds to `i` for this category.

### virtual const char \* std::error\_category::name () const` [pure virtual]`, ` [noexcept]`

A string that identifies the error category.

### bool std::error\_category::operator\< (const error\_category & \_\_other) const` [inline]`, ` [noexcept]`

Ordered comparison that defines a total order for error categories.

### bool std::error\_category::operator== (const error\_category & \_\_other) const` [inline]`, ` [noexcept]`

An error\_category only compares equal to itself.

## Author

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