如何在C ++中解析字符串

Question

I want to parse the strings, so that to check whether they have specified syntax or not.

Example:

Str = Z344-R565l t

Here my requirement is after Z there should be a number and after that a - and after that R should be there followed by a number, followed by l , followed by a space and then finally t .

If any thing other than this it should be a error.

I have to parse many different kind of syntax like this. I would be awkward if write a function for each type of syntax required. I heard that yacc or lex can solve this problem.

Can any one please throw some light on my problem?

Answer 1

You do this with a regex.

Z344-R565l t

Your regex should look something like this. Not sure what regex library to use for c++, but this is the general regex to make sure that your string matches.

Z[0-9]+-R[0-9]+l t

Answer 2

Use boost::regex

#include <string>
#include <boost/regex.hpp>

bool isMatch(std::string input){
    boost::regex r("Z[0-9]*-R[0-9]*l t");
    return boost::regex_search(input, r);
}

The other thing that you could do is supply a list of regex expressions in a file, one expression per line. Create a vector of boost::regex objects using the file input and iterate through the vector of patterns for each string you need to validate. It's not very efficient but it will work.

Answer 3

Boost::Regex is fine if you just want to check the syntax. If you want to actually do something when you read such an expression, i suggest you use Boost::Spirit with something like :

rule<> testFormula = 
    (ch_p('Z') >> int_p) 
    >> (ch_p('-')>>ch_p('R')>>int_p>>ch_p('l')) 
    >> space_p >> ch_p('t');

I have isolated parts of the expression which you might want to connect to some action (using [] operator).

See the documentation for more information

Answer 4

If you have a recent compiler (VC 2008 SP1, etc.), there's no need to use boost, regex are part of TR1 and you can use them with this header: #include <regex>

Example for a date ( you should use double \\ as escape character ):

string dateorder = "12/07/2009";

tr1::regex expr("^([1-2][0-9]|0?[1-9]|30|31)/([1-9]|10|11|12)/(2\\\d{3})$");

if (!regex_match(dateorder.begin(),dateorder.end(),expr))
{
    ...
    break;  
}

Answer 5

You might google " runtime parser generation " or something similar...

lex and yacc (or their GNU equivaents flex and bison ) do their work at compile time and may not be flexible enough for your needs. (or they may, you're not very specific).