如何在C ++正则表达式中用大括号{匹配字符串 [英] How to match a string with an opening brace { in C++ regex

问题描述

我有关于用C ++编写正则表达式的知识.我有2个正则表达式，可以在Java中正常工作.但这就是抛出错误

I have about writing regexes in C++. I have 2 regexes which work fine in java. But these throws an error namely

 one of * + was not preceded by a valid regular expression C++

这些正则表达式如下:

 regex r1("^[\s]*{[\s]*\n"); //Space followed by '{' then followed by spaces and '\n'
 regex r2("^[\s]*{[\s]*\/\/.*\n") // Space followed by '{' then by  '//' and '\n'

有人可以帮助我如何解决此错误或用C ++重新编写这些正则表达式吗?

Can someone help me how to fix this error or re-write these regex in C++?

推荐答案

请参见 basic_regex参考:

默认情况下，正则表达式模式遵循 ECMAScript语法.

ECMAScript语法参考指出:

字符: \ 字符
说明:字符
matches (匹配):字符字符本身，而无需在正则表达式中解释其特殊含义.除构成上述任何特殊字符序列的字符外，任何字符都可以转义. 需要: ^ $ \ . * + ? ( ) [ ] { } |

characters: \character
description: character
matches: the character character as it is, without interpreting its special meaning within a regex expression. Any character can be escaped except those which form any of the special character sequences above. Needed for: ^ $ \ . * + ? ( ) [ ] { } |

因此，您需要转义 {才能使代码正常工作:

So, you need to escape { to get the code working:

std::string s("\r\n  { \r\nSome text here");
regex r1(R"(^\s*\{\s*\n)");
regex r2(R"(^\s*\{\s*//.*\n)");
std::string newtext = std::regex_replace( s, r1, "" );
std::cout << newtext << std::endl;

请参见 IDEONE演示

此外，请注意 R(pattern_here_with_single_escaping_backslashes)" 原始字符串文字语法如何简化正则表达式声明.

Also, note how the R"(pattern_here_with_single_escaping_backslashes)" raw string literal syntax simplifies a regex declaration.

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