---
name: "std::__ctype_abstract_base"
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::__ctype_abstract_base"
---

# std::\_\_ctype\_abstract\_base(3)

Common base for ctype facet.

## NAME

std::\_\_ctype\_abstract\_base\< \_CharT \> - Common base for ctype facet.

## SYNOPSIS

\#include \<locale\>

Inherits **std::locale::facet**, and **std::ctype\_base**.

Inherited by **std::mask\< \_CharT \>**, **std::ctype\< char \>**, and **std::ctype\< \_CharT \>**.

### Public Types

typedef const int \* **\_\_to\_type**\
 typedef \_CharT **char\_type**\
 Typedef for the template parameter.  typedef unsigned short **mask**\

### Public Member Functions

const **char\_type** \* **is** (const **char\_type** \*\_\_lo, const **char\_type** \*\_\_hi, mask \*\_\_vec) const\
 Return a mask array.  bool **is** (mask \_\_m, **char\_type** \_\_c) const\
 Test char\_type classification.  char **narrow** (**char\_type** \_\_c, char \_\_dfault) const\
 Narrow char\_type to char.  const **char\_type** \* **narrow** (const **char\_type** \*\_\_lo, const **char\_type** \*\_\_hi, char \_\_dfault, char \*\_\_to) const\
 Narrow array to char array.  const **char\_type** \* **scan\_is** (mask \_\_m, const **char\_type** \*\_\_lo, const **char\_type** \*\_\_hi) const\
 Find char\_type matching a mask.  const **char\_type** \* **scan\_not** (mask \_\_m, const **char\_type** \*\_\_lo, const **char\_type** \*\_\_hi) const\
 Find char\_type not matching a mask.  const **char\_type** \* **tolower** (**char\_type** \*\_\_lo, const **char\_type** \*\_\_hi) const\
 Convert array to lowercase.  **char\_type** **tolower** (**char\_type** \_\_c) const\
 Convert to lowercase.  const **char\_type** \* **toupper** (**char\_type** \*\_\_lo, const **char\_type** \*\_\_hi) const\
 Convert array to uppercase.  **char\_type** **toupper** (**char\_type** \_\_c) const\
 Convert to uppercase.  **char\_type** **widen** (char \_\_c) const\
 Widen char to char\_type.  const char \* **widen** (const char \*\_\_lo, const char \*\_\_hi, **char\_type** \*\_\_to) const\
 Widen array to char\_type.

### Static Public Attributes

static const mask **alnum**\
 static const mask **alpha**\
 static const mask **blank**\
 static const mask **cntrl**\
 static const mask **digit**\
 static const mask **graph**\
 static const mask **lower**\
 static const mask **print**\
 static const mask **punct**\
 static const mask **space**\
 static const mask **upper**\
 static const mask **xdigit**\

### Protected Member Functions

**\_\_ctype\_abstract\_base** (size\_t \_\_refs=0)\
 virtual const **char\_type** \* **do\_is** (const **char\_type** \*\_\_lo, const **char\_type** \*\_\_hi, mask \*\_\_vec) const =0\
 Return a mask array.  virtual bool **do\_is** (mask \_\_m, **char\_type** \_\_c) const =0\
 Test char\_type classification.  virtual char **do\_narrow** (**char\_type** \_\_c, char \_\_dfault) const =0\
 Narrow char\_type to char.  virtual const **char\_type** \* **do\_narrow** (const **char\_type** \*\_\_lo, const **char\_type** \*\_\_hi, char \_\_dfault, char \*\_\_to) const =0\
 Narrow char\_type array to char.  virtual const **char\_type** \* **do\_scan\_is** (mask \_\_m, const **char\_type** \*\_\_lo, const **char\_type** \*\_\_hi) const =0\
 Find char\_type matching mask.  virtual const **char\_type** \* **do\_scan\_not** (mask \_\_m, const **char\_type** \*\_\_lo, const **char\_type** \*\_\_hi) const =0\
 Find char\_type not matching mask.  virtual const **char\_type** \* **do\_tolower** (**char\_type** \*\_\_lo, const **char\_type** \*\_\_hi) const =0\
 Convert array to lowercase.  virtual **char\_type** **do\_tolower** (**char\_type** \_\_c) const =0\
 Convert to lowercase.  virtual const **char\_type** \* **do\_toupper** (**char\_type** \*\_\_lo, const **char\_type** \*\_\_hi) const =0\
 Convert array to uppercase.  virtual **char\_type** **do\_toupper** (**char\_type** \_\_c) const =0\
 Convert to uppercase.  virtual **char\_type** **do\_widen** (char \_\_c) const =0\
 Widen char.  virtual const char \* **do\_widen** (const char \*\_\_lo, const char \*\_\_hi, **char\_type** \*\_\_to) const =0\
 Widen char array.

### Static Protected Member Functions

static \_\_c\_locale **\_S\_clone\_c\_locale** (\_\_c\_locale &\_\_cloc)  throw ()\
 static void **\_S\_create\_c\_locale** (\_\_c\_locale &\_\_cloc, const char \*\_\_s, \_\_c\_locale \_\_old=0)\
 static void **\_S\_destroy\_c\_locale** (\_\_c\_locale &\_\_cloc)\
 static \_\_c\_locale **\_S\_get\_c\_locale** ()\
 static const char \* **\_S\_get\_c\_name** ()  throw ()\
 static \_\_c\_locale **\_S\_lc\_ctype\_c\_locale** (\_\_c\_locale \_\_cloc, const char \*\_\_s)\

## Detailed Description

### template\<typename \_CharT\>

class std::\_\_ctype\_abstract\_base\< \_CharT \>"Common base for ctype facet.

This template class provides implementations of the public functions that forward to the protected virtual functions.

This template also provides abstract stubs for the protected virtual functions.

## Member Typedef Documentation

### template\<typename \_CharT\> typedef \_CharT std::\_\_ctype\_abstract\_base\< \_CharT \>::char\_type

Typedef for the template parameter.

## Member Function Documentation

### template\<typename \_CharT\> virtual const char\_type \* std::\_\_ctype\_abstract\_base\< \_CharT \>::do\_is (const char\_type \* \_\_lo, const char\_type \* \_\_hi, mask \* \_\_vec) const \[protected\], \[pure virtual\]

Return a mask array. This function finds the mask for each char\_type in the range \[lo,hi) and successively writes it to vec. vec must have as many elements as the input.

do\_is() is a hook for a derived facet to change the behavior of classifying. do\_is() must always return the same result for the same input.

**Parameters**

*\_\_lo* Pointer to start of range. \
 *\_\_hi* Pointer to end of range. \
 *\_\_vec* Pointer to an array of mask storage.

**Returns**

*\_\_hi*.

Implemented in **std::ctype\< \_CharT \>**, and **std::mask\< \_CharT \>**.

### template\<typename \_CharT\> virtual bool std::\_\_ctype\_abstract\_base\< \_CharT \>::do\_is (mask \_\_m, char\_type \_\_c) const \[protected\], \[pure virtual\]

Test char\_type classification. This function finds a mask M for *c* and compares it to mask *m*.

do\_is() is a hook for a derived facet to change the behavior of classifying. do\_is() must always return the same result for the same input.

**Parameters**

*\_\_c* The char\_type to find the mask of. \
 *\_\_m* The mask to compare against.

**Returns**

(M & \_\_m) != 0.

Implemented in **std::ctype\< \_CharT \>**, **std::ctype\< wchar\_t \>**, and **std::mask\< \_CharT \>**.

Referenced by **std::mask\< \_CharT \>::is()**, and **std::mask\< \_CharT \>::is()**.

### template\<typename \_CharT\> virtual char std::\_\_ctype\_abstract\_base\< \_CharT \>::do\_narrow (char\_type \_\_c, char \_\_dfault) const \[protected\], \[pure virtual\]

Narrow char\_type to char. This virtual function converts the argument to char using the simplest reasonable transformation. If the conversion fails, dfault is returned instead.

do\_narrow() is a hook for a derived facet to change the behavior of narrowing. do\_narrow() must always return the same result for the same input.

Note: this is not what you want for codepage conversions. See codecvt for that.

**Parameters**

*\_\_c* The char\_type to convert. \
 *\_\_dfault* Char to return if conversion fails.

**Returns**

The converted char.

Implemented in **std::ctype\< \_CharT \>**, **std::ctype\< wchar\_t \>**, and **std::mask\< \_CharT \>**.

Referenced by **std::mask\< \_CharT \>::narrow()**, and **std::mask\< \_CharT \>::narrow()**.

### template\<typename \_CharT\> virtual const char\_type \* std::\_\_ctype\_abstract\_base\< \_CharT \>::do\_narrow (const char\_type \* \_\_lo, const char\_type \* \_\_hi, char \_\_dfault, char \* \_\_to) const \[protected\], \[pure virtual\]

Narrow char\_type array to char. This virtual function converts each char\_type in the range \[\_\_lo,\_\_hi) to char using the simplest reasonable transformation and writes the results to the destination array. For any element in the input that cannot be converted, *\_\_dfault* is used instead.

do\_narrow() is a hook for a derived facet to change the behavior of narrowing. do\_narrow() must always return the same result for the same input.

Note: this is not what you want for codepage conversions. See codecvt for that.

**Parameters**

*\_\_lo* Pointer to start of range. \
 *\_\_hi* Pointer to end of range. \
 *\_\_dfault* Char to use if conversion fails. \
 *\_\_to* Pointer to the destination array.

**Returns**

*\_\_hi*.

Implemented in **std::ctype\< \_CharT \>**, and **std::mask\< \_CharT \>**.

### template\<typename \_CharT\> virtual const char\_type \* std::\_\_ctype\_abstract\_base\< \_CharT \>::do\_scan\_is (mask \_\_m, const char\_type \* \_\_lo, const char\_type \* \_\_hi) const \[protected\], \[pure virtual\]

Find char\_type matching mask. This function searches for and returns the first char\_type c in \[\_\_lo,\_\_hi) for which is(\_\_m,c) is true.

do\_scan\_is() is a hook for a derived facet to change the behavior of match searching. do\_is() must always return the same result for the same input.

**Parameters**

*\_\_m* The mask to compare against. \
 *\_\_lo* Pointer to start of range. \
 *\_\_hi* Pointer to end of range.

**Returns**

Pointer to a matching char\_type if found, else *\_\_hi*.

Implemented in **std::ctype\< \_CharT \>**, **std::ctype\< wchar\_t \>**, and **std::mask\< \_CharT \>**.

Referenced by **std::mask\< \_CharT \>::scan\_is()**.

### template\<typename \_CharT\> virtual const char\_type \* std::\_\_ctype\_abstract\_base\< \_CharT \>::do\_scan\_not (mask \_\_m, const char\_type \* \_\_lo, const char\_type \* \_\_hi) const \[protected\], \[pure virtual\]

Find char\_type not matching mask. This function searches for and returns a pointer to the first char\_type c of \[lo,hi) for which is(m,c) is false.

do\_scan\_is() is a hook for a derived facet to change the behavior of match searching. do\_is() must always return the same result for the same input.

**Parameters**

*\_\_m* The mask to compare against. \
 *\_\_lo* Pointer to start of range. \
 *\_\_hi* Pointer to end of range.

**Returns**

Pointer to a non-matching char\_type if found, else *\_\_hi*.

Implemented in **std::ctype\< \_CharT \>**, **std::ctype\< wchar\_t \>**, and **std::mask\< \_CharT \>**.

Referenced by **std::mask\< \_CharT \>::scan\_not()**.

### template\<typename \_CharT\> virtual const char\_type \* std::\_\_ctype\_abstract\_base\< \_CharT \>::do\_tolower (char\_type \* \_\_lo, const char\_type \* \_\_hi) const \[protected\], \[pure virtual\]

Convert array to lowercase. This virtual function converts each char\_type in the range \[\_\_lo,\_\_hi) to lowercase if possible. Other elements remain untouched.

do\_tolower() is a hook for a derived facet to change the behavior of lowercasing. do\_tolower() must always return the same result for the same input.

**Parameters**

*\_\_lo* Pointer to start of range. \
 *\_\_hi* Pointer to end of range.

**Returns**

*\_\_hi*.

Implemented in **std::ctype\< \_CharT \>**, and **std::mask\< \_CharT \>**.

### template\<typename \_CharT\> virtual char\_type std::\_\_ctype\_abstract\_base\< \_CharT \>::do\_tolower (char\_type \_\_c) const \[protected\], \[pure virtual\]

Convert to lowercase. This virtual function converts the argument to lowercase if possible. If not possible (for example, '2'), returns the argument.

do\_tolower() is a hook for a derived facet to change the behavior of lowercasing. do\_tolower() must always return the same result for the same input.

**Parameters**

*\_\_c* The char\_type to convert.

**Returns**

The lowercase char\_type if convertible, else *\_\_c*.

Implemented in **std::ctype\< \_CharT \>**, **std::ctype\< wchar\_t \>**, and **std::mask\< \_CharT \>**.

Referenced by **std::mask\< \_CharT \>::tolower()**, and **std::mask\< \_CharT \>::tolower()**.

### template\<typename \_CharT\> virtual const char\_type \* std::\_\_ctype\_abstract\_base\< \_CharT \>::do\_toupper (char\_type \* \_\_lo, const char\_type \* \_\_hi) const \[protected\], \[pure virtual\]

Convert array to uppercase. This virtual function converts each char\_type in the range \[\_\_lo,\_\_hi) to uppercase if possible. Other elements remain untouched.

do\_toupper() is a hook for a derived facet to change the behavior of uppercasing. do\_toupper() must always return the same result for the same input.

**Parameters**

*\_\_lo* Pointer to start of range. \
 *\_\_hi* Pointer to end of range.

**Returns**

*\_\_hi*.

Implemented in **std::ctype\< \_CharT \>**, and **std::mask\< \_CharT \>**.

### template\<typename \_CharT\> virtual char\_type std::\_\_ctype\_abstract\_base\< \_CharT \>::do\_toupper (char\_type \_\_c) const \[protected\], \[pure virtual\]

Convert to uppercase. This virtual function converts the char\_type argument to uppercase if possible. If not possible (for example, '2'), returns the argument.

do\_toupper() is a hook for a derived facet to change the behavior of uppercasing. do\_toupper() must always return the same result for the same input.

**Parameters**

*\_\_c* The char\_type to convert.

**Returns**

The uppercase char\_type if convertible, else *\_\_c*.

Implemented in **std::ctype\< \_CharT \>**, **std::ctype\< wchar\_t \>**, and **std::mask\< \_CharT \>**.

Referenced by **std::mask\< \_CharT \>::toupper()**, and **std::mask\< \_CharT \>::toupper()**.

### template\<typename \_CharT\> virtual char\_type std::\_\_ctype\_abstract\_base\< \_CharT \>::do\_widen (char \_\_c) const \[protected\], \[pure virtual\]

Widen char. This virtual function converts the char to char\_type using the simplest reasonable transformation.

do\_widen() is a hook for a derived facet to change the behavior of widening. do\_widen() must always return the same result for the same input.

Note: this is not what you want for codepage conversions. See codecvt for that.

**Parameters**

*\_\_c* The char to convert.

**Returns**

The converted char\_type

Implemented in **std::ctype\< \_CharT \>**, **std::ctype\< char \>**, **std::ctype\< wchar\_t \>**, and **std::mask\< \_CharT \>**.

Referenced by **std::mask\< \_CharT \>::widen()**, and **std::mask\< \_CharT \>::widen()**.

### template\<typename \_CharT\> virtual const char \* std::\_\_ctype\_abstract\_base\< \_CharT \>::do\_widen (const char \* \_\_lo, const char \* \_\_hi, char\_type \* \_\_to) const \[protected\], \[pure virtual\]

Widen char array. This function converts each char in the input to char\_type using the simplest reasonable transformation.

do\_widen() is a hook for a derived facet to change the behavior of widening. do\_widen() must always return the same result for the same input.

Note: this is not what you want for codepage conversions. See codecvt for that.

**Parameters**

*\_\_lo* Pointer to start range. \
 *\_\_hi* Pointer to end of range. \
 *\_\_to* Pointer to the destination array.

**Returns**

*\_\_hi*.

Implemented in **std::ctype\< \_CharT \>**, and **std::mask\< \_CharT \>**.

### template\<typename \_CharT\> const char\_type \* std::\_\_ctype\_abstract\_base\< \_CharT \>::is (const char\_type \* \_\_lo, const char\_type \* \_\_hi, mask \* \_\_vec) const \[inline\]

Return a mask array. This function finds the mask for each char\_type in the range \[lo,hi) and successively writes it to vec. vec must have as many elements as the char array. It does so by returning the value of ctype\<char\_type\>::do\_is().

**Parameters**

*\_\_lo* Pointer to start of range. \
 *\_\_hi* Pointer to end of range. \
 *\_\_vec* Pointer to an array of mask storage.

**Returns**

*\_\_hi*.

### template\<typename \_CharT\> bool std::\_\_ctype\_abstract\_base\< \_CharT \>::is (mask \_\_m, char\_type \_\_c) const \[inline\]

Test char\_type classification. This function finds a mask M for *\_\_c* and compares it to mask *\_\_m*. It does so by returning the value of ctype\<char\_type\>::do\_is().

**Parameters**

*\_\_c* The char\_type to compare the mask of. \
 *\_\_m* The mask to compare against.

**Returns**

(M & \_\_m) != 0.

Referenced by **std::time\_get\< \_CharT, \_InIter \>::get()**.

### template\<typename \_CharT\> char std::\_\_ctype\_abstract\_base\< \_CharT \>::narrow (char\_type \_\_c, char \_\_dfault) const \[inline\]

Narrow char\_type to char. This function converts the char\_type to char using the simplest reasonable transformation. If the conversion fails, dfault is returned instead. It does so by returning ctype\<char\_type\>::do\_narrow(\_\_c).

Note: this is not what you want for codepage conversions. See codecvt for that.

**Parameters**

*\_\_c* The char\_type to convert. \
 *\_\_dfault* Char to return if conversion fails.

**Returns**

The converted char.

Referenced by **std::time\_get\< \_CharT, \_InIter \>::do\_get\_year()**, **std::time\_get\< \_CharT, \_InIter \>::get()**, and **std::time\_put\< \_CharT, \_OutIter \>::put()**.

### template\<typename \_CharT\> const char\_type \* std::\_\_ctype\_abstract\_base\< \_CharT \>::narrow (const char\_type \* \_\_lo, const char\_type \* \_\_hi, char \_\_dfault, char \* \_\_to) const \[inline\]

Narrow array to char array. This function converts each char\_type in the input to char using the simplest reasonable transformation and writes the results to the destination array. For any char\_type in the input that cannot be converted, *dfault* is used instead. It does so by returning ctype\<char\_type\>::do\_narrow(\_\_lo, \_\_hi, \_\_dfault, \_\_to).

Note: this is not what you want for codepage conversions. See codecvt for that.

**Parameters**

*\_\_lo* Pointer to start of range. \
 *\_\_hi* Pointer to end of range. \
 *\_\_dfault* Char to use if conversion fails. \
 *\_\_to* Pointer to the destination array.

**Returns**

*\_\_hi*.

### template\<typename \_CharT\> const char\_type \* std::\_\_ctype\_abstract\_base\< \_CharT \>::scan\_is (mask \_\_m, const char\_type \* \_\_lo, const char\_type \* \_\_hi) const \[inline\]

Find char\_type matching a mask. This function searches for and returns the first char\_type c in \[lo,hi) for which is(m,c) is true. It does so by returning ctype\<char\_type\>::do\_scan\_is().

**Parameters**

*\_\_m* The mask to compare against. \
 *\_\_lo* Pointer to start of range. \
 *\_\_hi* Pointer to end of range.

**Returns**

Pointer to matching char\_type if found, else *\_\_hi*.

### template\<typename \_CharT\> const char\_type \* std::\_\_ctype\_abstract\_base\< \_CharT \>::scan\_not (mask \_\_m, const char\_type \* \_\_lo, const char\_type \* \_\_hi) const \[inline\]

Find char\_type not matching a mask. This function searches for and returns the first char\_type c in \[lo,hi) for which is(m,c) is false. It does so by returning ctype\<char\_type\>::do\_scan\_not().

**Parameters**

*\_\_m* The mask to compare against. \
 *\_\_lo* Pointer to first char in range. \
 *\_\_hi* Pointer to end of range.

**Returns**

Pointer to non-matching char if found, else *\_\_hi*.

### template\<typename \_CharT\> const char\_type \* std::\_\_ctype\_abstract\_base\< \_CharT \>::tolower (char\_type \* \_\_lo, const char\_type \* \_\_hi) const \[inline\]

Convert array to lowercase. This function converts each char\_type in the range \[\_\_lo,\_\_hi) to lowercase if possible. Other elements remain untouched. It does so by returning ctype\<char\_type\>:: do\_tolower(\_\_lo, \_\_hi).

**Parameters**

*\_\_lo* Pointer to start of range. \
 *\_\_hi* Pointer to end of range.

**Returns**

*\_\_hi*.

### template\<typename \_CharT\> char\_type std::\_\_ctype\_abstract\_base\< \_CharT \>::tolower (char\_type \_\_c) const \[inline\]

Convert to lowercase. This function converts the argument to lowercase if possible. If not possible (for example, '2'), returns the argument. It does so by returning ctype\<char\_type\>::do\_tolower(c).

**Parameters**

*\_\_c* The char\_type to convert.

**Returns**

The lowercase char\_type if convertible, else *\_\_c*.

Referenced by **std::time\_get\< \_CharT, \_InIter \>::get()**.

### template\<typename \_CharT\> const char\_type \* std::\_\_ctype\_abstract\_base\< \_CharT \>::toupper (char\_type \* \_\_lo, const char\_type \* \_\_hi) const \[inline\]

Convert array to uppercase. This function converts each char\_type in the range \[lo,hi) to uppercase if possible. Other elements remain untouched. It does so by returning ctype\<char\_type\>:: do\_toupper(lo, hi).

**Parameters**

*\_\_lo* Pointer to start of range. \
 *\_\_hi* Pointer to end of range.

**Returns**

*\_\_hi*.

### template\<typename \_CharT\> char\_type std::\_\_ctype\_abstract\_base\< \_CharT \>::toupper (char\_type \_\_c) const \[inline\]

Convert to uppercase. This function converts the argument to uppercase if possible. If not possible (for example, '2'), returns the argument. It does so by returning ctype\<char\_type\>::do\_toupper().

**Parameters**

*\_\_c* The char\_type to convert.

**Returns**

The uppercase char\_type if convertible, else *\_\_c*.

Referenced by **std::time\_get\< \_CharT, \_InIter \>::get()**.

### template\<typename \_CharT\> char\_type std::\_\_ctype\_abstract\_base\< \_CharT \>::widen (char \_\_c) const \[inline\]

Widen char to char\_type. This function converts the char argument to char\_type using the simplest reasonable transformation. It does so by returning ctype\<char\_type\>::do\_widen(c).

Note: this is not what you want for codepage conversions. See codecvt for that.

**Parameters**

*\_\_c* The char to convert.

**Returns**

The converted char\_type.

Referenced by **std::money\_get\< \_CharT, \_InIter \>::do\_get()**, **std::time\_get\< \_CharT, \_InIter \>::do\_get()**, **std::money\_put\< \_CharT, \_OutIter \>::do\_put()**, and **std::time\_put\< \_CharT, \_OutIter \>::do\_put()**.

### template\<typename \_CharT\> const char \* std::\_\_ctype\_abstract\_base\< \_CharT \>::widen (const char \* \_\_lo, const char \* \_\_hi, char\_type \* \_\_to) const \[inline\]

Widen array to char\_type. This function converts each char in the input to char\_type using the simplest reasonable transformation. It does so by returning ctype\<char\_type\>::do\_widen(c).

Note: this is not what you want for codepage conversions. See codecvt for that.

**Parameters**

*\_\_lo* Pointer to start of range. \
 *\_\_hi* Pointer to end of range. \
 *\_\_to* Pointer to the destination array.

**Returns**

*\_\_hi*.

## Author

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