C ++ 11正则表达式可对数学表达式进行标记化 [英] C++11 regex to tokenize Mathematical Expression

问题描述

我有以下代码来标记格式为字符串的字符串:(1 + 2)/(((8))-(100 * 34):

I have the following code to tokenize a string of the format: (1+2)/((8))-(100*34):

如果用户使用不属于我的正则表达式的运算符或字符，我想向用户抛出错误.例如，如果用户输入3 ^ 4或x-6

I'd like to throw an error to the user if they use an operator or character that isn't part of my regex. e.g if user enters 3^4 or x-6

是否可以否定我的正则表达式，进行搜索，如果是真的，则抛出错误?

Is there a way to negate my regex, search for it and if it is true throw the error?

可以改善正则表达式的表达吗?

Can the regex expression be improved?

  //Using c++11 regex to tokenize input string
  //[0-9]+ = 1 or many digits
  //Or [\\-\\+\\\\\(\\)\\/\\*] = "-" or "+" or "/" or "*" or "(" or ")"
  std::regex e ( "[0-9]+|[\\-\\+\\\\\(\\)\\/\\*]");
  std::sregex_iterator rend;
  std::sregex_iterator a( infixExpression.begin(), infixExpression.end(), e );

  queue<string> infixQueue;
  while (a!=rend) {
      infixQueue.push(a->str());
      ++a;
  }
  return infixQueue;

-谢谢

推荐答案

您可以使用定义的搜索表达式 [^ 0-9()+ \-*/] 对字符串进行搜索作为C ++字符串，作为"[^ 0-9()+ \\-*/]" )，星号或斜杠.

You can run a search on the string using the search expression [^0-9()+\-*/] defined as C++ string as "[^0-9()+\\-*/]" which finds any character which is NOT a digit, a round bracket, a plus or minus sign (in real hyphen), an asterisk or a slash.

使用此正则表达式搜索字符串进行的搜索不应返回任何内容，否则该字符串包含不受支持的字符，例如 ^ 或 x .

The search with this regular expression search string should not return anything otherwise the string contains a not supported character like ^ or x.

[ ... ] 是肯定的字符类，这意味着找到一个字符，该字符是方括号中的字符之一.

[...] is a positive character class which means find a character being one of the characters in the square brackets.

[^ ... ] 是否定字符类，这意味着找到一个不是方括号中的字符之一的字符.

[^...] is a negative character class which means find a character NOT being one of the characters in the square brackets.

必须在方括号中转义才能被解释为文字字符的唯一字符是] ， \ 和-，其中-如果在方括号内的字符列表中是第一个或最后一个字符，则不得转义.但是，最好始终在方括号内转义-，因为这使正则表达式引擎/函数更容易检测到连字符应解释为文字字符，而不是"FROM x到z".

The only characters which must be escaped within square brackets to be interpreted as literal character are ], \ and - whereby - must not be escaped if being first or last character in the list of characters within the square brackets. But it is nevertheless better to escape - always within square brackets as this makes it easier for the regular expression engine / function to detect that the hyphen character should be interpreted as literal character and not with meaning "FROM x to z".

当然，此表达式不会检查缺少的右方括号.但是，与不需要使用基于输入的公式计算值的编译器或脚本解释器相比，公式分析器通常不需要与每个编译器相比，每个括号都必须有一个括号.

Of course this expression does not check for missing closing round brackets. But formula parsers do often not require that there is always a closing parenthesis for every opening parenthesis in comparison to a compiler or script interpreter simply because not needed to calculate the value based on entered formula.

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