Parse string using format template?

Question

If I can format a string using

string.Format("my {0} template {1} here", 1, 2) 

can I reverse the process - I provide the template and a filled-in string, .net returns arg0, arg1, etc.?

Answer 1

There's no elegant way to reverse the formatted string. But you can try this if you want a simple function.

private List<string> reverseStringFormat(string template, string str) {      //Handles regex special characters.     template = Regex.Replace(template, @"[\\\^\$\.\|\?\*\+\(\)]", m => "\\"       + m.Value);      string pattern = "^" + Regex.Replace(template, @"\{[0-9]+\}", "(.*?)") + "$";              Regex r = new Regex(pattern);     Match m = r.Match(str);      List<string> ret = new List<string>();      for (int i = 1; i < m.Groups.Count; i++)     {         ret.Add(m.Groups[i].Value);     }      return ret; } 

Answer 2

String.Format is not reversable in general case.

If you have exactly one {0} it is actaully possible to write generic code that at least extract string representation of the value. You definitely can't reverse it to produce original objects.

Samples:

1. Multiple arguments: string.Format("my{0}{1}", "aa", "aaa"); produces "myaaaaa", tring to reverse string.ReverseFormat("my{0}{1}", "myaaaaa") have to decide how to split "aaaaa" portion in 2 without any information.

2. Inability to reverse to data type string.Format("{0:yyyy}", DateTime.Now); results in 2011, most of information about value itself lost.