Extracting first token from a delimeted string

Question

i have a string: e.g. WORD1_WORD2_WORD3

how do i get just WORD1 from the string? i.e the text before the first underscore

Answer 1

It may be tempting to say Split - but that involves the creating of an array and lots of individual strings. IMO, the optimal way here is to find the first underscore, and take a substring:

string b = s.Substring(0, s.IndexOf('_')); // assumes at least one _

(edit)

If you are doing this lots, you could add some extension methods:

public static string SubstringBefore(this string s, char value) {
    if(string.IsNullOrEmpty(s)) return s;
    int i = s.IndexOf(value);
    return i > 0 ? s.Substring(0,i) : s;
}
public static string SubstringAfter(this string s, char value) {
    if (string.IsNullOrEmpty(s)) return s;
    int i = s.IndexOf(value);
    return i >= 0 ? s.Substring(i + 1) : s;
}

then:

string s = "a_b_c";
string b = s.SubstringBefore('_'), c = s.SubstringAfter('_');

Answer 2

YOUR_STRING.Split('_')[0]

In fact the Split method returns an array of strings resulting from splitting the original string at any occurrence of the specified character(s), not including the character at which the split was performed.