---
name: "std::basic_regex"
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::basic_regex"
---

# std::basic\_regex(3)

A regular expression.

## NAME

std::basic\_regex\< \_Ch\_type, \_Rx\_traits \> - A regular expression.

## SYNOPSIS

\#include \<regex\>

### Public Types

typedef **regex\_constants::syntax\_option\_type** **flag\_type**\
 typedef traits\_type::locale\_type **locale\_type**\
 typedef traits\_type::string\_type **string\_type**\
 typedef \_Rx\_traits **traits\_type**\
 typedef \_Ch\_type **value\_type**\

### Public Member Functions

**basic\_regex** () noexcept\
 template\<typename \_FwdIter\> **basic\_regex** (\_FwdIter \_\_first, \_FwdIter \_\_last, **flag\_type** \_\_f=ECMAScript)\
 Constructs a basic regular expression from the range \[first, last) interpreted according to the flags in f.  **basic\_regex** (basic\_regex &&\_\_rhs) noexcept=default\
 Move-constructs a basic regular expression.  **basic\_regex** (const \_Ch\_type \*\_\_p, **flag\_type** \_\_f=ECMAScript)\
 Constructs a basic regular expression from the sequence \[\_\_p, \_\_p + char\_traits\<\_Ch\_type\>::length(\_\_p)) interpreted according to the flags in \_\_f.  **basic\_regex** (const \_Ch\_type \*\_\_p, std::size\_t \_\_len, **flag\_type** \_\_f=ECMAScript)\
 Constructs a basic regular expression from the sequence \[p, p + len) interpreted according to the flags in f.  **basic\_regex** (const basic\_regex &\_\_rhs)=default\
 Copy-constructs a basic regular expression.  template\<typename \_Ch\_traits, typename \_Ch\_alloc\> **basic\_regex** (const **std::basic\_string**\< \_Ch\_type, \_Ch\_traits, \_Ch\_alloc \> &\_\_s, **flag\_type** \_\_f=ECMAScript)\
 Constructs a basic regular expression from the string s interpreted according to the flags in f.  **basic\_regex** (**initializer\_list**\< \_Ch\_type \> \_\_l, **flag\_type** \_\_f=ECMAScript)\
 Constructs a basic regular expression from an initializer list.  **~basic\_regex** ()\
 Destroys a basic regular expression.  template\<typename \_InputIterator\> **basic\_regex** & **assign** (\_InputIterator \_\_first, \_InputIterator \_\_last, **flag\_type** \_\_flags=ECMAScript)\
 Assigns a new regular expression to a regex object.  **basic\_regex** & **assign** (**basic\_regex** &&\_\_rhs) noexcept\
 Move-assigns one regular expression to another.  **basic\_regex** & **assign** (const \_Ch\_type \*\_\_p, **flag\_type** \_\_flags=ECMAScript)\
 Assigns a new regular expression to a regex object from a C-style null-terminated string containing a regular expression pattern.  **basic\_regex** & **assign** (const \_Ch\_type \*\_\_p, size\_t \_\_len, **flag\_type** \_\_flags=ECMAScript)\
 Assigns a new regular expression to a regex object from a C-style string containing a regular expression pattern.  **basic\_regex** & **assign** (const **basic\_regex** &\_\_rhs) noexcept\
 Assigns one regular expression to another.  template\<typename \_Ch\_traits, typename \_Alloc\> **basic\_regex** & **assign** (const **basic\_string**\< \_Ch\_type, \_Ch\_traits, \_Alloc \> &\_\_s, **flag\_type** \_\_flags=ECMAScript)\
 Assigns a new regular expression to a regex object from a string containing a regular expression pattern.  **basic\_regex** & **assign** (**initializer\_list**\< \_Ch\_type \> \_\_l, **flag\_type** \_\_flags=ECMAScript)\
 Assigns a new regular expression to a regex object.  **flag\_type** **flags** () const noexcept\
 Gets the flags used to construct the regular expression or in the last call to assign().  locale\_type **getloc** () const noexcept\
 Gets the locale currently imbued in the regular expression object.  locale\_type **imbue** (locale\_type \_\_loc)\
 Imbues the regular expression object with the given locale.  unsigned int **mark\_count** () const noexcept\
 Gets the number of marked subexpressions within the regular expression.  **basic\_regex** & **operator=** (**basic\_regex** &&)=default\
 Move-assigns one regular expression to another.  **basic\_regex** & **operator=** (const \_Ch\_type \*\_\_p)\
 Replaces a regular expression with a new one constructed from a C-style null-terminated string.  **basic\_regex** & **operator=** (const **basic\_regex** &)=default\
 Assigns one regular expression to another.  template\<typename \_Ch\_traits, typename \_Alloc\> **basic\_regex** & **operator=** (const **basic\_string**\< \_Ch\_type, \_Ch\_traits, \_Alloc \> &\_\_s)\
 Replaces a regular expression with a new one constructed from a string.  **basic\_regex** & **operator=** (**initializer\_list**\< \_Ch\_type \> \_\_l)\
 Replaces a regular expression with a new one constructed from an initializer list.  void **swap** (**basic\_regex** &\_\_rhs) noexcept\
 Swaps the contents of two regular expression objects.

### Static Public Attributes

**Constants**\
 std \[28.8.1\](1)

static constexpr **flag\_type** **icase**\
 static constexpr **flag\_type** **nosubs**\
 static constexpr **flag\_type** **optimize**\
 static constexpr **flag\_type** **collate**\
 static constexpr **flag\_type** **ECMAScript**\
 static constexpr **flag\_type** **basic**\
 static constexpr **flag\_type** **extended**\
 static constexpr **flag\_type** **awk**\
 static constexpr **flag\_type** **grep**\
 static constexpr **flag\_type** **egrep**\
 static constexpr **flag\_type** **multiline**\

### Friends

template\<typename \_Bp, typename \_Ap, typename \_Cp, typename \_Rp\> bool **\_\_detail::\_\_regex\_algo\_impl** (\_Bp, \_Bp, **match\_results**\< \_Bp, \_Ap \> &, const **basic\_regex**\< \_Cp, \_Rp \> &, **regex\_constants::match\_flag\_type**, \_\_detail::\_RegexExecutorPolicy, bool)\
 template\<typename, typename, typename\> class **\_\_detail::\_Executor**\

### Related Symbols

(Note that these are not member symbols.)  template\<typename \_Ch\_type, typename \_Rx\_traits\> void **swap** (**basic\_regex**\< \_Ch\_type, \_Rx\_traits \> &\_\_lhs, **basic\_regex**\< \_Ch\_type, \_Rx\_traits \> &\_\_rhs) noexcept\
 Swaps the contents of two regular expression objects.

## Detailed Description

### template\<typename \_Ch\_type, typename \_Rx\_traits = regex\_traits\<\_Ch\_type\>\>

class std::basic\_regex\< \_Ch\_type, \_Rx\_traits \>"A regular expression.

Specializations of this class template represent regular expressions constructed from sequences of character type \_Ch\_type. Use the std::regex typedef for std::basic\_regex\<char\>.

A character sequence passed to the constructor will be parsed according to the chosen grammar, and used to create a state machine representing the regular expression. The regex object can then be passed to algorithms such as std::regex\_match to match sequences of characters.

The syntax\_option\_type flag passed to the constructor selects from one of the supported regular expression grammars. The default is ECMAScript and the others are basic, extended, awk, grep, and egrep, which are variations on POSIX regular expressions.

**Since**

C++11

## Constructor & Destructor Documentation

### template\<typename \_Ch\_type, typename \_Rx\_traits = regex\_traits\<\_Ch\_type\>\> std::basic\_regex\< \_Ch\_type, \_Rx\_traits \>::basic\_regex () \[inline\], \[noexcept\]

Constructs a basic regular expression that does not match any character sequence.

### template\<typename \_Ch\_type, typename \_Rx\_traits = regex\_traits\<\_Ch\_type\>\> std::basic\_regex\< \_Ch\_type, \_Rx\_traits \>::basic\_regex (const \_Ch\_type \* \_\_p, flag\_type \_\_f = ECMAScript) \[inline\], \[explicit\]

Constructs a basic regular expression from the sequence \[\_\_p, \_\_p + char\_traits\<\_Ch\_type\>::length(\_\_p)) interpreted according to the flags in \_\_f.

**Parameters**

*\_\_p* A pointer to the start of a C-style null-terminated string containing a regular expression. \
 *\_\_f* Flags indicating the syntax rules and options.

**Exceptions**

**regex\_error if** \_\_p **is not a valid regular expression.**

### template\<typename \_Ch\_type, typename \_Rx\_traits = regex\_traits\<\_Ch\_type\>\> std::basic\_regex\< \_Ch\_type, \_Rx\_traits \>::basic\_regex (const \_Ch\_type \* \_\_p, std::size\_t \_\_len, flag\_type \_\_f = ECMAScript) \[inline\]

**Constructs a basic regular expression from the sequence \[p, p + len) interpreted according to the flags in** f**.**

**Parameters**

*\_\_p* **A pointer to the start of a string containing a regular expression.** \
 *\_\_len* **The length of the string containing the regular expression.** \
 *\_\_f* **Flags indicating the syntax rules and options.**

**Exceptions**

**regex\_error if** \_\_p **is not a valid regular expression.**

### template\<typename \_Ch\_type, typename \_Rx\_traits = regex\_traits\<\_Ch\_type\>\> std::basic\_regex\< \_Ch\_type, \_Rx\_traits \>::basic\_regex (const basic\_regex\< \_Ch\_type, \_Rx\_traits \> & \_\_rhs) \[default\]

**Copy-constructs a basic regular expression.**

**Parameters**

*\_\_rhs* **A** regex **object.**

### template\<typename \_Ch\_type, typename \_Rx\_traits = regex\_traits\<\_Ch\_type\>\> std::basic\_regex\< \_Ch\_type, \_Rx\_traits \>::basic\_regex (basic\_regex\< \_Ch\_type, \_Rx\_traits \> && \_\_rhs) \[default\], \[noexcept\]

**Move-constructs a basic regular expression.**

**Parameters**

*\_\_rhs* **A** regex **object.**

### template\<typename \_Ch\_type, typename \_Rx\_traits = regex\_traits\<\_Ch\_type\>\> template\<typename \_Ch\_traits, typename \_Ch\_alloc\> std::basic\_regex\< \_Ch\_type, \_Rx\_traits \>::basic\_regex (const std::basic\_string\< \_Ch\_type, \_Ch\_traits, \_Ch\_alloc \> & \_\_s, flag\_type \_\_f = ECMAScript) \[inline\], \[explicit\]

**Constructs a basic regular expression from the string** s **interpreted according to the flags in** f**.**

**Parameters**

*\_\_s* **A string containing a regular expression.** \
 *\_\_f* **Flags indicating the syntax rules and options.**

**Exceptions**

**regex\_error if** \_\_s **is not a valid regular expression.**

### template\<typename \_Ch\_type, typename \_Rx\_traits = regex\_traits\<\_Ch\_type\>\> template\<typename \_FwdIter\> std::basic\_regex\< \_Ch\_type, \_Rx\_traits \>::basic\_regex (\_FwdIter \_\_first, \_FwdIter \_\_last, flag\_type \_\_f = ECMAScript) \[inline\]

**Constructs a basic regular expression from the range \[first, last) interpreted according to the flags in** f**.**

**Parameters**

*\_\_first* **The start of a range containing a valid regular expression.** \
 *\_\_last* **The end of a range containing a valid regular expression.** \
 *\_\_f* **The format flags of the regular expression.**

**Exceptions**

**regex\_error if \[\_\_first, \_\_last) is not a valid regular expression.**

### template\<typename \_Ch\_type, typename \_Rx\_traits = regex\_traits\<\_Ch\_type\>\> std::basic\_regex\< \_Ch\_type, \_Rx\_traits \>::basic\_regex (initializer\_list\< \_Ch\_type \> \_\_l, flag\_type \_\_f = ECMAScript) \[inline\]

**Constructs a basic regular expression from an initializer list.**

**Parameters**

*\_\_l* **The initializer list.** \
 *\_\_f* **The format flags of the regular expression.**

**Exceptions**

**regex\_error if** \_\_l **is not a valid regular expression.**

### template\<typename \_Ch\_type, typename \_Rx\_traits = regex\_traits\<\_Ch\_type\>\> std::basic\_regex\< \_Ch\_type, \_Rx\_traits \>::~basic\_regex () \[inline\]

**Destroys a basic regular expression.**

## Member Function Documentation

### template\<typename \_Ch\_type, typename \_Rx\_traits = regex\_traits\<\_Ch\_type\>\> template\<typename \_InputIterator\> basic\_regex & std::basic\_regex\< \_Ch\_type, \_Rx\_traits \>::assign (\_InputIterator \_\_first, \_InputIterator \_\_last, flag\_type \_\_flags = ECMAScript) \[inline\]

**Assigns a new regular expression to a regex object.**

**Parameters**

*\_\_first* **The start of a range containing a valid regular expression.** \
 *\_\_last* **The end of a range containing a valid regular expression.** \
 *\_\_flags* **Syntax option flags.**

**Exceptions**

**regex\_error if p does not contain a valid regular expression pattern interpreted according to** \_\_flags**. If regex\_error is thrown, the object remains unchanged.**

### template\<typename \_Ch\_type, typename \_Rx\_traits = regex\_traits\<\_Ch\_type\>\> basic\_regex & std::basic\_regex\< \_Ch\_type, \_Rx\_traits \>::assign (basic\_regex\< \_Ch\_type, \_Rx\_traits \> && \_\_rhs) \[inline\], \[noexcept\]

**Move-assigns one regular expression to another.**

**Parameters**

*\_\_rhs* **Another regular expression object.**

### template\<typename \_Ch\_type, typename \_Rx\_traits = regex\_traits\<\_Ch\_type\>\> basic\_regex & std::basic\_regex\< \_Ch\_type, \_Rx\_traits \>::assign (const \_Ch\_type \* \_\_p, flag\_type \_\_flags = ECMAScript) \[inline\]

**Assigns a new regular expression to a regex object from a C-style null-terminated string containing a regular expression pattern.**

**Parameters**

*\_\_p* **A pointer to a C-style null-terminated string containing a regular expression pattern.** \
 *\_\_flags* **Syntax option flags.**

**Exceptions**

**regex\_error if \_\_p does not contain a valid regular expression pattern interpreted according to** \_\_flags**. If regex\_error is thrown, \*this remains unchanged.**

### template\<typename \_Ch\_type, typename \_Rx\_traits = regex\_traits\<\_Ch\_type\>\> basic\_regex & std::basic\_regex\< \_Ch\_type, \_Rx\_traits \>::assign (const \_Ch\_type \* \_\_p, size\_t \_\_len, flag\_type \_\_flags = ECMAScript) \[inline\]

**Assigns a new regular expression to a regex object from a C-style string containing a regular expression pattern.**

**Parameters**

*\_\_p* **A pointer to a C-style string containing a regular expression pattern.** \
 *\_\_len* **The length of the regular expression pattern string.** \
 *\_\_flags* **Syntax option flags.**

**Exceptions**

**regex\_error if p does not contain a valid regular expression pattern interpreted according to** \_\_flags**. If regex\_error is thrown, \*this remains unchanged.**

### template\<typename \_Ch\_type, typename \_Rx\_traits = regex\_traits\<\_Ch\_type\>\> basic\_regex & std::basic\_regex\< \_Ch\_type, \_Rx\_traits \>::assign (const basic\_regex\< \_Ch\_type, \_Rx\_traits \> & \_\_rhs) \[inline\], \[noexcept\]

**Assigns one regular expression to another.**

**Parameters**

*\_\_rhs* **Another regular expression object.**

**Referenced by std::basic\_regex\< char \>::basic\_regex(), std::basic\_regex\< char \>::assign(), std::basic\_regex\< char \>::operator=(), std::basic\_regex\< char \>::operator=(), and std::basic\_regex\< char \>::operator=().**

### template\<typename \_Ch\_type, typename \_Rx\_traits = regex\_traits\<\_Ch\_type\>\> template\<typename \_Ch\_traits, typename \_Alloc\> basic\_regex & std::basic\_regex\< \_Ch\_type, \_Rx\_traits \>::assign (const basic\_string\< \_Ch\_type, \_Ch\_traits, \_Alloc \> & \_\_s, flag\_type \_\_flags = ECMAScript) \[inline\]

**Assigns a new regular expression to a regex object from a string containing a regular expression pattern.**

**Parameters**

*\_\_s* **A string containing a regular expression pattern.** \
 *\_\_flags* **Syntax option flags.**

**Exceptions**

**regex\_error if \_\_s does not contain a valid regular expression pattern interpreted according to** \_\_flags**. If regex\_error is thrown, \*this remains unchanged.**

### template\<typename \_Ch\_type, typename \_Rx\_traits = regex\_traits\<\_Ch\_type\>\> basic\_regex & std::basic\_regex\< \_Ch\_type, \_Rx\_traits \>::assign (initializer\_list\< \_Ch\_type \> \_\_l, flag\_type \_\_flags = ECMAScript) \[inline\]

**Assigns a new regular expression to a regex object.**

**Parameters**

*\_\_l* **An initializer list representing a regular expression.** \
 *\_\_flags* **Syntax option flags.**

**Exceptions**

**regex\_error if** \_\_l **does not contain a valid regular expression pattern interpreted according to** \_\_flags**. If regex\_error is thrown, the object remains unchanged.**

### template\<typename \_Ch\_type, typename \_Rx\_traits = regex\_traits\<\_Ch\_type\>\> flag\_type std::basic\_regex\< \_Ch\_type, \_Rx\_traits \>::flags () const \[inline\], \[noexcept\]

**Gets the flags used to construct the regular expression or in the last call to assign().**

### template\<typename \_Ch\_type, typename \_Rx\_traits = regex\_traits\<\_Ch\_type\>\> locale\_type std::basic\_regex\< \_Ch\_type, \_Rx\_traits \>::getloc () const \[inline\], \[noexcept\]

**Gets the locale currently imbued in the regular expression object.**

### template\<typename \_Ch\_type, typename \_Rx\_traits = regex\_traits\<\_Ch\_type\>\> locale\_type std::basic\_regex\< \_Ch\_type, \_Rx\_traits \>::imbue (locale\_type \_\_loc) \[inline\]

**Imbues the regular expression object with the given locale.**

**Parameters**

*\_\_loc* **A locale.**

### template\<typename \_Ch\_type, typename \_Rx\_traits = regex\_traits\<\_Ch\_type\>\> unsigned int std::basic\_regex\< \_Ch\_type, \_Rx\_traits \>::mark\_count () const \[inline\], \[noexcept\]

**Gets the number of marked subexpressions within the regular expression.**

### template\<typename \_Ch\_type, typename \_Rx\_traits = regex\_traits\<\_Ch\_type\>\> basic\_regex & std::basic\_regex\< \_Ch\_type, \_Rx\_traits \>::operator= (basic\_regex\< \_Ch\_type, \_Rx\_traits \> && ) \[default\]

**Move-assigns one regular expression to another.**

### template\<typename \_Ch\_type, typename \_Rx\_traits = regex\_traits\<\_Ch\_type\>\> basic\_regex & std::basic\_regex\< \_Ch\_type, \_Rx\_traits \>::operator= (const \_Ch\_type \* \_\_p) \[inline\]

**Replaces a regular expression with a new one constructed from a C-style null-terminated string.**

**Parameters**

*\_\_p* **A pointer to the start of a null-terminated C-style string containing a regular expression.**

### template\<typename \_Ch\_type, typename \_Rx\_traits = regex\_traits\<\_Ch\_type\>\> basic\_regex & std::basic\_regex\< \_Ch\_type, \_Rx\_traits \>::operator= (const basic\_regex\< \_Ch\_type, \_Rx\_traits \> & ) \[default\]

**Assigns one regular expression to another.**

### template\<typename \_Ch\_type, typename \_Rx\_traits = regex\_traits\<\_Ch\_type\>\> template\<typename \_Ch\_traits, typename \_Alloc\> basic\_regex & std::basic\_regex\< \_Ch\_type, \_Rx\_traits \>::operator= (const basic\_string\< \_Ch\_type, \_Ch\_traits, \_Alloc \> & \_\_s) \[inline\]

**Replaces a regular expression with a new one constructed from a string.**

**Parameters**

*\_\_s* **A pointer to a string containing a regular expression.**

### template\<typename \_Ch\_type, typename \_Rx\_traits = regex\_traits\<\_Ch\_type\>\> basic\_regex & std::basic\_regex\< \_Ch\_type, \_Rx\_traits \>::operator= (initializer\_list\< \_Ch\_type \> \_\_l) \[inline\]

**Replaces a regular expression with a new one constructed from an initializer list.**

**Parameters**

*\_\_l* **The initializer list.**

**Exceptions**

**regex\_error if** \_\_l **is not a valid regular expression.**

### template\<typename \_Ch\_type, typename \_Rx\_traits = regex\_traits\<\_Ch\_type\>\> void std::basic\_regex\< \_Ch\_type, \_Rx\_traits \>::swap (basic\_regex\< \_Ch\_type, \_Rx\_traits \> & \_\_rhs) \[inline\], \[noexcept\]

**Swaps the contents of two regular expression objects.**

**Parameters**

*\_\_rhs* **Another regular expression object.**

## Author

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