此正则表达式无法解析所有有效的浮点数 [英] this regular expression fail to parse all valid floating numbers
问题描述
我正在尝试查找所有浮点数(可以是带 -/+ 前缀或不带 -/+ 前缀的指数形式).例如，以下是有效格式:-1.2 +1.2 .2 -3 3E4 -3e5 e-5
I am trying to find all floating number (could be in exponential forms with -/+ prefix or not). For example, the following is the valid format: -1.2 +1.2 .2 -3 3E4 -3e5 e-5
文本源包含多个以空格或逗号分隔的数字.我需要用正则表达式来告诉
The source of text contains several numbers separated with space or comma. I need to use regular expression to tell
- 判断是否有任何无效数字(例如 1.2 3.2 s3) s3 不是有效数字
- 列出每个有效数字
我不知道如何完成 (1) 但对于 (2)，我使用的是 boost::regex 和以下代码
I have no idea how to get (1) done but for (2), I am using boost::regex and the following code
wstring strre("[-+]?\\b[0-9]*\\.?[0-9]+(?:[eE][-+]?[0-9]+)?\\b");
wstring src("1.2 -3.4 3.2 3 2 1e-3 3e3");
boost::wregex regexp(strre);
boost::match_results<std::wstring::const_iterator> what;
regex_search(src, what, regexp, boost::match_continuous);
wcout << "RE: " << strre << endl << endl;
wcout << "SOURCE: [" << src << "]" << endl;
for (int i=0; i<what.size(); i++)
wcout << "OUTPUT: [" << wstring(what[i].first, what[i].second) << "]"<< endl;
但是这段代码只显示了第一个数字(1.2).我也试过 boost::match_all、boost::match_default，结果一样.
But this code only show me the first number (1.2). I also try boost::match_all, boost::match_default, the same result.
附加信息:大家好，让我们不要担心双反斜杠问题，它在我的代码中正确表达(因为在我的测试代码中，我不是通过显式字符串从文本中读取字符串).无论如何，我修改代码如下
ADDITIONAL INFO: Hi all, let's not worry about double backslash issue, it is correctly expressed in my code (because in my testing code, I read the string from a text not by explicit string). Anyway, I modify the code as follow
wstring strre("[-+]?\\b[0-9]*\\.?[0-9]+(?:[eE][-+]?[0-9]+)?\\b");
boost::wregex regexp(strre);
boost::match_results<std::wstring::const_iterator> what;
wcout << "RE: " << strre << endl << endl;
while (src.length()>0)
{
wcout << "SOURCE: [" << src << "]" << endl;
regex_search(src, what, regexp, boost::match_default);
wcout << "OUTPUT: [" << wstring(what[0].first, what[0].second) << endl;
src = wstring(what[0].second, src.end());
}
现在，它正确地显示了所有单个数字，但我必须多次运行 regex_search，因为它一次只给出一个数字.好吧，我只是不明白为什么 regex_search 不会给我所有的结果.有没有办法运行一次搜索并返回所有结果?
Now, it is correctly show everything single numbers but I have to run regex_search several time due to it only give one number at a time. Well, I just don't understand why regex_search won't give me all results instead. Is that any way to run the search once and get all the results back?
推荐答案
您通常必须对 C++ 字符串中的内容进行双重转义.所以你的 "\." 变成了 ..你需要它是 "\\." 等.同样，你的 "\b" 不是一个字边界，而是一个文字退格！以同样的方式修复:"\\b".
You normally have to double-escape backslash things in a C++ string. So your "\." turns into just .. You would need it to be "\\.", etc. Similarly, your "\b" becomes not a word-boundary but rather a literal backspace! Fix the same way: "\\b".
另外，那个 strre 类的文档在哪里?您确定它理解您使用的语言吗?
Also, where’s the doc for that strre class? Are you sure it understands the language you are using?
显然，新的 C++ 标准具有原始字符串文字.这些就像 Go 中的反引号"字符串，或者像 Perl 中的单引号"字符串或/patterns/.有关详细信息，请参阅此答案.
Apparently the new C++ standard has raw string literals. These work like `backticked` strings in Go, or like 'single-quoted' strings or /patterns/ in Perl. See this answer for details.
这里有一种更高级的检测浮点文字的模式，但不使用反斜杠:
Here’s a somewhat fancier pattern for detecting floating-point literals, but which uses no backslashes:
[+-]?(?=[.]?[0-9])[0-9]*(?:[.][0-9]*)?(?:[Ee][+-]?[0-9]+)?
请注意，它确实需要前瞻，而 ERE 不支持.您可能应该使用 PCRE 库，它确实如此.分解，那是
Note that it does require lookaheads, which EREs don’t support. You should probably use the PCRE library, which does. Broken down, that’s
[+-]? # optional leading sign
(?=[.]?[0-9]) # lookahead for a digit, maybe with an intervening dot
[0-9]* # maybe some digits
(?:[.][0-9]*)? # maybe a (dot plus maybe some digits)
(?:[Ee][+-]?[0-9]+)? # maybe an exponent, which may have a sign and must have digits
模式由 Perl 的 Regexp::Common 库提供.
Pattern courtesy of Perl’s Regexp::Common library.
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