如何在使用Regex.Replace方法时找到子字符串？

Question

I'm using this code to replace all found values in string by indexes:

int i = 0;
input = "FGS1=(B+A*10)+A*10+(C*10.5)";
Regex r = new Regex("([A-Z][A-Z\\d]*)");
bool f = false;
MatchEvaluator me = delegate(Match m)
{
  f = true;
  i++;
  return "i" + i.ToString();
};
do { f = false; input = r.Replace(input, me); } while (f);
//expected result: input == "i1=(i2+i3*10)+i4*10+(i5*10.5)"

But i have to do it in more complex way, for what i have to do something with found value. For example:

MatchEvaluator me = delegate(Match m)
{
  foundValue = /*getting value*/;
  if (foundValue = "A") i--;
  f = true;
  i++;
  return "i" + i.ToString();
};

Expected result for this code: "i1=(i2+i2*10)+i2*10+(i3*10.5)"

Answer 1

You can use the Groups collection in the match object to get the matched groups. The first item is the entire match, so the value from the first group is at index 1:

string foundValue = m.Groups[1].Value;
if (foundValue == "A") i--;

Answer 2

Guessing you need to implement a variable assignment in which you assign ix (where x is an incrementing number) to each variable and then reuse this value if it appears, we can write the following code to solve your problem:

var identifiers = new Dictionary<string, string>();
int i = 0;
var input = "FGS1=(B+A*10)+A*10+(C*10.5)";
Regex r = new Regex("([A-Z][A-Z\\d]*)");
bool f = false;

MatchEvaluator me = delegate(Match m)
{
    var variableName = m.ToString();

    if(identifiers.ContainsKey(variableName)){
        return identifiers[variableName];
    }
    else {
        i++;
        var newVariableName = "i" + i.ToString();
        identifiers[variableName] = newVariableName;
        return newVariableName;
    }
};

input = r.Replace(input, me);
Console.WriteLine(input);

This code should print: i1=(i2+i3*10)+i3*10+(i4*10.5)

Answer 3

Your question should be answered by Guffa already, just want to share my alternative way to solve your problem, using more feature from .NET Regex (If I understand your problem correctly):

int i = 1;
string input = "FGS1=(B+A*10)+A*10+(C*10.5)";   
var lookUp = new Dictionary<string, string>();
var output = Regex.Replace(input, 
             "([A-Z][A-Z\\d]*)", 
             m => { 
                if(!lookUp.ContainsKey(m.Value))
                {           
                    lookUp[m.Value] = "i" + i++;            
                }
                return lookUp[m.Value]; 
            });
Console.WriteLine(output);      //i1=(i2+i3*10)+i3*10+(i4*10.5)

I use a dictionary to keep track of which matched is repeated

This should work even if your repeated matched is different from "A". In your original solution, it checks specifically for "A", which is quite fragile