c++11特性之正则表达式
最后更新于：2022-04-01 06:31:57
C++11中也将正则表达式纳入了新标准的一部分，不仅如此，它还支持了6种不同的正则表达式的语法，分别是：`ECMASCRIPT`、`basic`、`extended`、`awk`、`grep和egrep`。其中`ECMASCRIPT`是默认的语法，具体使用哪种语法我们可以在构造正则表达式的时候指定。
正则表达式库提供表示正则表达式，这是一种用于字符串内执行模式匹配小型的语言的类。
主要的类：
**basic_regex**
regular expression object
**sub_match**
identifies the sequence of characters matched by a sub-expression
**match_results**
identifies one regular expression match, including all sub-expression matches
算法：
These functions are used to apply the regular expression encapsulated in a regex to a target sequence of characters.
**regex_match**
attempts to match a regular expression to an entire character sequence
**regex_search**
attempts to match a regular expression to any part of a character sequence
**regex_replace**
replaces occurrences of a regular expression with formatted replacement text
迭代器：
The regex iterators are used to traverse the entire set of regular expression matches found within a sequence.
**regex_iterator**
iterates through all regex matches within a character sequence
**regex_token_iterator**
iterates through the specified sub-expressions within all regex matches in a given string or through unmatched substrings
异常：
This class defines the type of objects thrown as exceptions to report errors from the regular expressions library.
**regex_error**
reports errors generated by the regular expressions library
例子代码：
~~~
#include <iostream>
#include <iterator>
#include <string>
#include <regex>
int main()
{
std::string s = "Some people, when confronted with a problem, think "
"\"I know, I'll use regular expressions.\" "
"Now they have two problems.";
std::regex self_regex("REGULAR EXPRESSIONS",
std::regex_constants::ECMAScript | std::regex_constants::icase);
if (std::regex_search(s, self_regex)) {
std::cout << "Text contains the phrase 'regular expressions'\n";
}
std::regex word_regex("(\\S+)");
auto words_begin =
std::sregex_iterator(s.begin(), s.end(), word_regex);
auto words_end = std::sregex_iterator();
std::cout << "Found "
<< std::distance(words_begin, words_end)
<< " words\n";
const int N = 6;
std::cout << "Words longer than " << N << " characters:\n";
for (std::sregex_iterator i = words_begin; i != words_end; ++i) {
std::smatch match = *i;
std::string match_str = match.str();
if (match_str.size() > N) {
std::cout << " " << match_str << '\n';
}
}
std::regex long_word_regex("(\\w{7,})");
std::string new_s = std::regex_replace(s, long_word_regex, "[$&]");
std::cout << new_s << '\n';
}
Output:
Text contains the phrase 'regular expressions'
Found 19 words
Words longer than 6 characters:
people,
confronted
problem,
regular
expressions."
problems.
Some people, when [confronted] with a [problem], think
"I know, I'll use [regular] [expressions]." Now they have two [problems].
~~~