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只是一个示例代码C++ Primer 5th Edition: 17.3.3. Using the Regular Expression Library

主文件main.cpp：

#include <iostream>
#include "regexcase.h"
using namespace std;

int main() {
    using_regex();
    return 0;
}

头文件regexcase.h：

#ifndef REGEXCASE_H_
#define REGEXCASE_H_

#include <regex>
#include <string>

void using_regex();
std::string parseCode(std::regex_constants::error_type etype);

#endif /* REGEXCASE_H_ */

源文件regexcase.cpp：

#include "regexcase.h"
#include <iostream>
using namespace std;

void using_regex() {
    // look for words that violate a well-known spelling rule of thumb, "i before e, except after c":
    // find the characters ei that follow a character other than c
    string pattern("[^c]ei");
    // we want the whole word in which our pattern appears
    pattern = "[a-zA-Z]*" + pattern + "[a-zA-Z]*";  //[a-zA-Z]*   [[:alpha:]]*
    try {
        regex r(pattern, regex_constants::extended);    // construct a regex to find pattern                // , regex_constants::extended
        smatch results;     // define an object to hold the results of a search
        // define a string that has text that does and doesn't match pattern
        string test_str = "receipt freind theif receive";
        // use r to find a match to pattern in test_str
        if (regex_search(test_str, results, r)) // if there is a match
            cout << results.str() << endl;      // print the matching word
        else
            cout << "no match for " << pattern << endl;
    } catch (regex_error &e) {
        cout << "what: " << e.what() << "; code: " << parseCode(e.code()) << endl;
    }
}

string parseCode(regex_constants::error_type etype) {
    switch (etype) {
    case regex_constants::error_collate:
        return "error_collate: invalid collating element request";
    case regex_constants::error_ctype:
        return "error_ctype: invalid character class";
    case regex_constants::error_escape:
        return "error_escape: invalid escape character or trailing escape";
    case regex_constants::error_backref:
        return "error_backref: invalid back reference";
    case regex_constants::error_brack:
        return "error_brack: mismatched bracket([ or ])";
    case regex_constants::error_paren:
        return "error_paren: mismatched parentheses(( or ))";
    case regex_constants::error_brace:
        return "error_brace: mismatched brace({ or })";
    case regex_constants::error_badbrace:
        return "error_badbrace: invalid range inside a { }";
    case regex_constants::error_range:
        return "erro_range: invalid character range(e.g., [z-a])";
    case regex_constants::error_space:
        return "error_space: insufficient memory to handle this regular expression";
    case regex_constants::error_badrepeat:
        return "error_badrepeat: a repetition character (*, ?, +, or {) was not preceded by a valid regular expression";
    case regex_constants::error_complexity:
        return "error_complexity: the requested match is too complex";
    case regex_constants::error_stack:
        return "error_stack: insufficient memory to evaluate a match";
    default:
        return "";
    }
}

调用的输出using_regex();是what: regex_error; code: error_brack: mismatched bracket([ or ])

似乎正则表达式无法解析括号。

参考这个问题的答案，我regex_constants::extended用来初始化正则表达式对象，然后是regex r(pattern, regex_constants::extended);

然后输出是no match for [[:alpha:]]*[^c]ei[[:alpha:]]*

似乎正则表达式无法匹配模式。

然后我用[a-zA-Z]*替换字符类[[:alpha:]]*（regex_constants::extended仍然设置）。输出仍然是no match for [a-zA-Z]*[^c]ei[a-zA-Z]*

平台：windows

使用的工具：Eclipse for C/C++;MinGW (g++ --version: g++ 4.7.2)

编辑：感谢@sharth，添加主文件以完成代码。

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1 回答 1

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我刚刚使用 libc++ 和 clang++ 进行了测试。这按预期工作。这是我的主要内容：

int main() {
    string test_str = "receipt freind theif receive";
    string pattern = "[a-zA-Z]*[^c]ei[a-zA-Z]*";

    try {
        regex r(pattern, regex_constants::extended);
        smatch results;

        if (regex_search(test_str, results, r))
            cout << results.str() << endl;
        else
            cout << "no match for " << pattern << endl;
    } catch (regex_error &e) {
        cout << "what: " << e.what() << "; code: " << parseCode(e.code()) << endl;
    }
}

输出：

freind

另一方面，GCC 4.7.2 给出了这个结果：

no match for [a-zA-Z]*[^c]ei[a-zA-Z]*

这是因为在 GCC 4.7.2 的 libstdc++ 中，它们仍然没有实现正则表达式。这是 的实现regex_search：

template<typename _Bi_iter, typename _Allocator, typename _Ch_type, typename _Rx_traits>
inline bool regex_search(_Bi_iter __first, _Bi_iter __last, match_results<_Bi_iter, _Allocator>& __m, const basic_regex<_Ch_type, _Rx_traits>& __re, regex_constants::match_flag_type __flags) {
    return false;
}

需要注意的是，包含一个读者可以编译的小程序非常有帮助。这样就不会混淆正在运行的代码。

于 2013-02-08T16:12:43.117 回答