I have string. "12341234115151_log_1.txt" (this string length is not fixed. but "log" pattern always same) I have a for loop. each iteration, I want to set the number after "log" of i.
like "12341234115151_log_2.txt" "12341234115151_log_3.txt" ....
to "12341234115151_log_123.txt"
in c#, what is a good way to do so? thanks.
A regex is ideal for this. You can use the Regex.Replace method and use a MatchEvaluator delegate to perform the numerical increment.
string input = "12341234115151_log_1.txt";
string pattern = @"(\d+)(?=\.)";
string result = Regex.Replace(input, pattern,
m => (int.Parse(m.Groups[1].Value) + 1).ToString());
The pattern breakdown is as follows:
(\d+): this matches and captures any digit, at least once(?=\.): this is a look-ahead which ensures that a period (or dot) follows the number. A dot must be escaped to be a literal dot instead of a regex metacharacter. We know that the value you want to increment is right before the ".txt" so it should always have a dot after it. You could also use (?=\.txt) to make it clearer and be explicit, but you may have to use RegexOptions.IgnoreCase if your filename extension can have different cases.You can use Regex. like this
var r = new Regex("^(.*_log_)(\\d).txt$")
for ... {
var newname = r.Replace(filename, "${1}"+i+".txt");
}
Use regular expressions to get the counter, then just append them together.
If I've read your question right...
How about,
for (int i =0; i<some condition; i++)
{
string name = "12341234115151_log_"+ i.ToString() + ".txt";
}
12341234115151_log_1.txt,12341234115151_log_12.txt, 12341234115151_log_123.txt, 12341234115151_log_1234.txtetc?