1、正则表达式
（1）regex的匹配和查找接口
#include <regex>
#include <iostream>
using namespace std;void out (bool b)
{cout << ( b ? "found" : "not found") << endl;
}int main()
{// find XML/HTML-tagged value (using default syntax):regex reg1("<.*>.*</.*>");bool found = regex_match ("<tag>value</tag>", // datareg1); // regular expressionout(found);// find XML/HTML-tagged value (tags before and after the value must match):regex reg2("<(.*)>.*</\\1>");found = regex_match ("<tag>value</tag>", // datareg2); // regular expressionout(found);// find XML/HTML-tagged value (using grep syntax):regex reg3("<\\(.*\\)>.*</\\1>",regex_constants::grep);found = regex_match ("<tag>value</tag>", // datareg3); // regular expressionout(found);// use C-string as regular expression (needs explicit cast to regex):found = regex_match ("<tag>value</tag>", // dataregex("<(.*)>.*</\\1>")); // regular expressionout(found);cout << endl;// regex_match() versus regex_search():found = regex_match ("XML tag: <tag>value</tag>", regex("<(.*)>.*</\\1>")); // fails to matchout(found);found = regex_match ("XML tag: <tag>value</tag>", regex(".*<(.*)>.*</\\1>.*")); // matchesout(found);found = regex_search ("XML tag: <tag>value</tag>", regex("<(.*)>.*</\\1>")); // matchesout(found);found = regex_search ("XML tag: <tag>value</tag>", regex(".*<(.*)>.*</\\1>.*")); // matchesout(found);
}
输出：
found
found
found
foundnot found
found
found
foundregex_match()检验是否整个字符序列匹配某个正则表达式。
regex_search()检验是否部分字符序列匹配某个正则表达式。
regex_match(data, regex(pattern))
总是等价于
regex_search(data, regex("(.|\n)*" + pattern + "(.|\n)*"))，其中(.|\n)*指任何数量和任意字符，.意指换行之外的任意字符，|表示or。
（2）处理次表达式
#include <string>
#include <regex>
#include <iostream>
#include <iomanip>
using namespace std;int main()
{string data = "XML tag: <tag-name>the value</tag-name>.";cout << "data: " << data << "\n\n";smatch m; // for returned details of the matchbool found = regex_search (data,m, regex("<(.*)>(.*)</(\\1)>")); //出现\1则是代表与第一个小括号中要匹配的内容相同。// print match details:cout << "m.empty(): " << boolalpha << m.empty() << endl;cout << "m.size(): " << m.size() << endl;if (found) {cout << "m.str(): " << m.str() << endl;cout << "m.length(): " << m.length() << endl;cout << "m.position(): " << m.position() << endl;cout << "m.prefix().str(): " << m.prefix().str() << endl;cout << "m.suffix().str(): " << m.suffix().str() << endl;cout << endl;// iterating over all matches (using the match index):for (int i=0; i<m.size(); ++i) {cout << "m[" << i << "].str(): " << m[i].str() << endl;cout << "m.str(" << i << "): " << m.str(i) << endl;cout << "m.position(" << i << "): " << m.position(i)<< endl;}cout << endl;// iterating over all matches (using iterators):cout << "matches:" << endl;for (auto pos = m.begin(); pos != m.end(); ++pos) {cout << " " << *pos << " ";cout << "(length: " << pos->length() << ")" << endl;}}
}
输出：
data: XML tag: <tag-name>the value</tag-name>.m.empty(): false
m.size(): 4
m.str(): <tag-name>the value</tag-name>
m.length(): 30
m.position(): 9
m.prefix().str(): XML tag:
m.suffix().str(): .m[0].str(): <tag-name>the value</tag-name>
m.str(0): <tag-name>the value</tag-name>
m.position(0): 9
m[1].str(): tag-name
m.str(1): tag-name
m.position(1): 10
m[2].str(): the value
m.str(2): the value
m.position(2): 19
m[3].str(): tag-name
m.str(3): tag-name
m.position(3): 30matches:<tag-name>the value</tag-name> (length: 30)tag-name (length: 8)the value (length: 9)tag-name (length: 8)smatch:针对“匹配string”而设计
cmatch:针对“匹配C-string（const char*）”而设计
wsmatch:针对“匹配wstring”而设计
wcmatch:针对“匹配wide C-string（const wchar_t*）”而设计
出现\1则是代表与第一个小括号中要匹配的内容相同。注意：\1必须与小括号配合使用
（3）regex iterator
#include <string>
#include <regex>
#include <iostream>
#include <algorithm>
using namespace std;int main()
{string data = "<person>\n"" <first>Nico</first>\n"" <last>Josuttis</last>\n""</person>\n";regex reg("<(.*)>(.*)</(\\1)>");// iterate over all matches (using a regex_iterator):sregex_iterator pos(data.cbegin(),data.cend(),reg);sregex_iterator end;for ( ; pos!=end ; ++pos ) {cout << "match: " << pos->str() << endl;cout << " tag: " << pos->str(1) << endl;cout << " value: " << pos->str(2) << endl;}// use a regex_iterator to process each matched substring as element in an algorithm:sregex_iterator beg(data.cbegin(),data.cend(),reg);for_each (beg,end,[](const smatch& m) {cout << "match: " << m.str() << endl;cout << " tag: " << m.str(1) << endl;cout << " value: " << m.str(2) << endl;});
}
输出：
match: <first>Nico</first>tag: firstvalue: Nico
match: <last>Josuttis</last>tag: lastvalue: Josuttis
match: <first>Nico</first>tag: firstvalue: Nico
match: <last>Josuttis</last>tag: lastvalue: Josuttis（4）regex token iterator
#include <string>
#include <regex>
#include <iostream>
#include <algorithm>
using namespace std;int main()
{string data = "<person>\n"" <first>Nico</first>\n"" <last>Josuttis</last>\n""</person>\n";regex reg("<(.*)>(.*)</(\\1)>");// iterate over all matches (using a regex_token_iterator):sregex_token_iterator pos(data.cbegin(),data.cend(), // sequencereg, // token separator{0,2}); // 0: full match, 2: second substringsregex_token_iterator end;for ( ; pos!=end ; ++pos ) {cout << "match: " << pos->str() << endl;}cout << endl;string names = "nico, jim, helmut, paul, tim, john paul, rita";regex sep("[ \t\n]*[,;.][ \t\n]*"); // separated by , ; or . and spacessregex_token_iterator p(names.cbegin(),names.cend(), // sequencesep, // separator-1); // -1: values between separatorssregex_token_iterator e;for ( ; p!=e ; ++p ) {cout << "name: " << *p << endl;}
}
输出：
match: <first>Nico</first>
match: Nico
match: <last>Josuttis</last>
match: Josuttisname: nico
name: jim
name: helmut
name: paul
name: tim
name: john paul
name: rita（5）用于替换的正则表达式
#include <string>
#include <regex>
#include <iostream>
#include <iterator>using namespace std;int main() {string data = "<person>\n"" <first>Nico</first>\n"" <last>Josuttis</last>\n""</person>\n";regex reg("<(.*)>(.*)</(\\1)>");cout << regex_replace(data,reg, "<$1 value=\"$2\"/>") << endl; //replacementcout << regex_replace(data,reg,"<\\1 value=\"\\2\"/>",regex_constants::format_sed) << endl;string res2;regex_replace(back_inserter(res2),data.begin(), data.end(),reg,"<$1 value=\"$2\"/>",regex_constants::format_no_copy | regex_constants::format_first_only);cout << res2 << endl;return 0;
}
输出：
<person><first value="Nico"/><last value="Josuttis"/>
</person><person><first value="Nico"/><last value="Josuttis"/>
</person><first value="Nico"/>
（6）regex flag
#include <string>
#include <regex>
#include <iostream>
using namespace std;int main()
{// case-insensitive find LaTeX index entriesstring pat1 = R"(\\.*index\{([^}]*)\})"; // first capture groupstring pat2 = R"(\\.*index\{(.*)\}\{(.*)\})"; // 2nd and 3rd capture groupregex pat (pat1+"\n"+pat2,regex_constants::egrep|regex_constants::icase);// initialize string with characters from standard input:string data((istreambuf_iterator<char>(cin)),istreambuf_iterator<char>());// search and print matching index entries:smatch m;auto pos = data.cbegin();auto end = data.cend();for ( ; regex_search (pos,end,m,pat); pos=m.suffix().first) {cout << "match: " << m.str() << endl;cout << " val: " << m.str(1)+m.str(2) << endl;cout << " see: " << m.str(3) << endl;}
}
（7）regex 异常
#include <regex>
#include <string>template <typename T>
std::string regexCode (T code)
{switch (code) {case std::regex_constants::error_collate:return "error_collate: ""regex has invalid collating element name";case std::regex_constants::error_ctype:return "error_ctype: ""regex has invalid character class name";case std::regex_constants::error_escape:return "error_escape: ""regex has invalid escaped char. or trailing escape";case std::regex_constants::error_backref:return "error_backref: ""regex has invalid back reference";case std::regex_constants::error_brack:return "error_brack: ""regex has mismatched '[' and ']'";case std::regex_constants::error_paren:return "error_paren: ""regex has mismatched '(' and ')'";case std::regex_constants::error_brace:return "error_brace: ""regex has mismatched '{' and '}'";case std::regex_constants::error_badbrace:return "error_badbrace: ""regex has invalid range in {} expression";case std::regex_constants::error_range:return "error_range: ""regex has invalid character range, such as '[b-a]'";case std::regex_constants::error_space:return "error_space: ""insufficient memory to convert regex into finite state";case std::regex_constants::error_badrepeat:return "error_badrepeat: ""one of *?+{ not preceded by valid regex";case std::regex_constants::error_complexity:return "error_complexity: ""complexity of match against regex over pre-set level";case std::regex_constants::error_stack:return "error_stack: ""insufficient memory to determine regex match";}return "unknown/non-standard regex error code";
}#include <regex>
#include <iostream>
#include "regexexception.hpp"
using namespace std;int main()
{try {// initialize regular expression with invalid syntax:regex pat ("\\\\.*index\\{([^}]*)\\}",regex_constants::grep|regex_constants::icase);//...}catch (const regex_error& e) {cerr << "regex_error: \n"<< " what(): " << e.what() << "\n"<< " code(): " << regexCode(e.code()) << endl;}
}（8）regex ECMAScript文法
![[笔记] wsl 下使用 qemu/grub 模拟系统启动(单分区)](https://img-blog.csdnimg.cn/direct/8bed4119a5bb41d88abfb3eb64595186.png)
