CODEWITHSUNDEEP
c#
user1848850
user1848850

Reputation: 463

C# TrimStart weird behaviour

Hey guys just wanted to understand something here.

I have this code:

        var testString = "DA DDDLY DO:DAXS      D/B#BTN A   TIME/DTE:0027/01NOV";
        var testTrimStart = testString.TrimStart("DA ".ToCharArray());

testTrimStart outputs:

LY DO:DAXS D/B#BTN A TIME/DTE:0027/01NOV

Could someone explain why

DA DDD

is removed.

I could understand if it was

DA DA DDDLY DO....

I understand it's an array of type CHAR that it's searching for. But should it not be searching and replacing

"DA "

throughout the string?

Here's the .NET FIDDLE Link

Upvotes: 1

Views: 188

Answers (1)

Lasse V. Karlsen
Lasse V. Karlsen

Reputation: 391336

You said:

  • Trim away every character from the start of the string that is either a 'D', a 'A', or a space.

The behavior of TrimStart is documented in the documentation:

Removes all leading occurrences of a set of characters specified in an array from the current String object.

(my emphasis)

Basically the TrimStart method is this in pseudocode:

if first character of string is either a 'D', a 'A', or a space
    then remove that character
    and repeat this algorithm for the next character (which is now the first)

The actual implementation is more optimal than this but this is how you could sum it up.

If you meant this:

Remove this specific substring from the start of the string if it is present

Then there are 2 ways of doing that:

  • Use a regex

    Regex.Replace(testString, "^DA ", string.Empty);

  • Look for it yourself using substring and comparison

    if (testString.StartsWith("DA "))
    testString = testString.Substring(3); // 3 == length of "DA "

If you this:

  • A simple replace

then you have no guarantee that the replacement will occur at the very start of the string.

Upvotes: 4

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