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basic_regex Class

  • Grein

Wraps a regular expression.

Syntax

template <class Elem, class RXtraits>
class basic_regex

Parameters

Elem
The type of elements to match.

RXtraits
Traits class for elements.

Remarks

The class template describes an object that holds a regular expression. Objects of this class template can be passed to the template functions regex_match, regex_search, and regex_replace. It also passes the suitable text string arguments, to search for text that matches the regular expression. There are two specializations of this class template, with the type definitions regex for elements of type char, and wregex for elements of type wchar_t.

The template argument RXtraits describes various important properties of the syntax of the regular expressions that the class template supports. A class that specifies these regular expression traits must have the same external interface as an object of type regex_traits Class.

Some functions take an operand sequence that defines a regular expression. You can specify such an operand sequence several ways:

ptr: a null-terminated sequence (such as a C string, for Elem of type char) beginning at ptr (which must not be a null pointer), where the terminating element is the value value_type() and isn't part of the operand sequence

ptr, count: a sequence of count elements beginning at ptr (which must not be a null pointer)

str: the sequence specified by the basic_string object str

first, last: a sequence of elements delimited by the iterators first and last, in the range [first, last)

right: the basic_regex object right

The above member functions also take an argument flags that specifies various options for the interpretation of the regular expression in addition to options described by the RXtraits type.

Members

Member Default Value
public static const flag_type icase regex_constants::icase
public static const flag_type nosubs regex_constants::nosubs
public static const flag_type optimize regex_constants::optimize
public static const flag_type collate regex_constants::collate
public static const flag_type ECMAScript regex_constants::ECMAScript
public static const flag_type basic regex_constants::basic
public static const flag_type extended regex_constants::extended
public static const flag_type awk regex_constants::awk
public static const flag_type grep regex_constants::grep
public static const flag_type egrep regex_constants::egrep
private RXtraits traits

Constructors

Constructor Description
basic_regex Construct the regular expression object.

Typedefs

Type name Description
flag_type The type of syntax option flags.
locale_type The type of the stored locale object.
value_type The element type.

Member functions

Member function Description
assign Assigns a value to the regular expression object.
flags Returns syntax option flags.
getloc Returns the stored locale object.
imbue Alters the stored locale object.
mark_count Returns number of subexpressions matched.
swap Swaps two regular expression objects.

Operators

Operator Description
operator= Assigns a value to the regular expression object.

Requirements

Header: <regex>

Namespace: std

Example

// std__regex__basic_regex.cpp
// compile with: /EHsc
#include <regex>
#include <iostream>

using namespace std;

int main()
{
    regex::value_type elem = 'x';
    regex::flag_type flag = regex::grep;

    elem = elem;  // to quiet "unused" warnings
    flag = flag;

    // constructors
    regex rx0;
    cout << "match(\"abc\", \"\") == " << boolalpha
        << regex_match("abc", rx0) << endl;

    regex rx1("abcd", regex::ECMAScript);
    cout << "match(\"abc\", \"abcd\") == " << boolalpha
        << regex_match("abc", rx1) << endl;

    regex rx2("abcd", 3);
    cout << "match(\"abc\", \"abc\") == " << boolalpha
        << regex_match("abc", rx2) << endl;

    regex rx3(rx2);
    cout << "match(\"abc\", \"abc\") == " << boolalpha
        << regex_match("abc", rx3) << endl;

    string str("abcd");
    regex rx4(str);
    cout << "match(string(\"abcd\"), \"abc\") == " << boolalpha
        << regex_match("abc", rx4) << endl;

    regex rx5(str.begin(), str.end() - 1);
    cout << "match(string(\"abc\"), \"abc\") == " << boolalpha
        << regex_match("abc", rx5) << endl;
    cout << endl;

    // assignments
    rx0 = "abc";
    rx0 = rx1;
    rx0 = str;

    rx0.assign("abcd", regex::ECMAScript);
    rx0.assign("abcd", 3);
    rx0.assign(rx1);
    rx0.assign(str);
    rx0.assign(str.begin(), str.end() - 1);

    rx0.swap(rx1);

    // mark_count
    cout << "\"abc\" mark_count == "
        << regex("abc").mark_count() << endl;
    cout << "\"(abc)\" mark_count == "
        << regex("(abc)").mark_count() << endl;

    // locales
    regex::locale_type loc = rx0.imbue(locale());
    cout << "getloc == imbued == " << boolalpha
        << (loc == rx0.getloc()) << endl;

    // initializer_list
    regex rx6({ 'a', 'b', 'c' }, regex::ECMAScript);
    cout << "match(\"abc\") == " << boolalpha
        << regex_match("abc", rx6);
    cout << endl;
}

match("abc", "") == false
match("abc", "abcd") == false
match("abc", "abc") == true
match("abc", "abc") == true
match(string("abcd"), "abc") == false
match(string("abc"), "abc") == true

"abc" mark_count == 0
"(abc)" mark_count == 1
getloc == imbued == true
match("abc") == true

basic_regex::assign

Assigns a value to the regular expression object.

basic_regex& assign(
    const basic_regex& right);

basic_regex& assign(
    const Elem* ptr,
    flag_type flags = ECMAScript);

basic_regex& assign(
    const Elem* ptr,
    size_type len,
    flag_type flags = ECMAScript);

basic_regex& assign(
    initializer_list<_Elem> IList,
    flag_type flags = regex_constants::ECMAScript);

template <class STtraits, class STalloc>
basic_regex& assign(
    const basic_string<Elem, STtraits, STalloc>& str,
    flag_type flags = ECMAScript);

template <class InIt>
basic_regex& assign(
    InIt first, InIt last,
    flag_type flags = ECMAScript);

Parameters

STtraits
Traits class for a string source.

STalloc
Allocator class for a string source.

InIt
Input iterator type for a range source.

right
Regex source to copy.

ptr
Pointer to beginning of sequence to copy.

flags
Syntax option flags to add while copying.

len/TD>
Length of sequence to copy.

str
String to copy.

first
Beginning of sequence to copy.

last
End of sequence to copy.

IList
The initializer_list to copy.

Remarks

The member functions each replace the regular expression held by *this with the regular expression described by the operand sequence, then return *this.

basic_regex::basic_regex

Construct the regular expression object.

basic_regex();

explicit basic_regex(
    const Elem* ptr,
    flag_type flags);

explicit basic_regex(
    const Elem* ptr,
    size_type len,
    flag_type flags);

basic_regex(
    const basic_regex& right);

basic_regex(
    initializer_list<Type> IList,
    flag_type flags);

template <class STtraits, class STalloc>
explicit basic_regex(
    const basic_string<Elem, STtraits, STalloc>& str,
    flag_type flags);

template <class InIt>
explicit basic_regex(
    InIt first,
    InIt last,
    flag_type flags);

Parameters

STtraits
Traits class for a string source.

STalloc
Allocator class for a string source.

InIt
Input iterator type for a range source.

right
Regex source to copy.

ptr
Pointer to beginning of sequence to copy.

flags
Syntax option flags to add while copying.

len/TD>
Length of sequence to copy.

str
String to copy.

first
Beginning of sequence to copy.

last
End of sequence to copy.

IList
The initializer_list to copy.

Remarks

All constructors store a default-constructed object of type RXtraits.

The first constructor constructs an empty basic_regex object. The other constructors construct a basic_regex object that holds the regular expression described by the operand sequence.

An empty basic_regex object doesn't match any character sequence when passed to regex_match, regex_search, or regex_replace.

basic_regex::flag_type

The type of syntax option flags.

typedef regex_constants::syntax_option_type flag_type;

Remarks

The type is a synonym for regex_constants::syntax_option_type.

basic_regex::flags

Returns syntax option flags.

flag_type flags() const;

Remarks

The member function returns the value of the flag_type argument passed to the most recent call to one of the basic_regex::assign member functions or, if no such call has been made, the value passed to the constructor.

basic_regex::getloc

Returns the stored locale object.

locale_type getloc() const;

Remarks

The member function returns traits.regex_traits::getloc().

basic_regex::imbue

Alters the stored locale object.

locale_type imbue(locale_type loc);

Parameters

loc
The locale object to store.

Remarks

The member function empties *this and returns traits.regex_traits::imbue(loc).

basic_regex::locale_type

The type of the stored locale object.

typedef typename RXtraits::locale_type locale_type;

Remarks

The type is a synonym for regex_traits::locale_type.

basic_regex::mark_count

Returns number of subexpressions matched.

unsigned mark_count() const;

Remarks

The member function returns the number of capture groups in the regular expression.

basic_regex::operator=

Assigns a value to the regular expression object.

basic_regex& operator=(const basic_regex& right);

basic_regex& operator=(const Elem *str);

template <class STtraits, class STalloc>
basic_regex& operator=(const basic_string<Elem, STtraits, STalloc>& str);

Parameters

STtraits
Traits class for a string source.

STalloc
Allocator class for a string source.

right
Regex source to copy.

str
String to copy.

Remarks

The operators each replace the regular expression held by *this with the regular expression described by the operand sequence, then return *this.

basic_regex::swap

Swaps two regular expression objects.

void swap(basic_regex& right) throw();

Parameters

right
The regular expression object to swap with.

Remarks

The member function swaps the regular expressions between *this and right. It does so in constant time and throws no exceptions.

basic_regex::value_type

The element type.

typedef Elem value_type;

Remarks

The type is a synonym for the template parameter Elem.

See also

<regex>
regex_match
regex_search
regex_replace
regex
wregex
regex_traits Class