CODEWITHSUNDEEP
c#
brgerner
brgerner

Reputation: 4371

Why does `String.Trim()` not trim the object itself?

Not often but sometimes I need to use String.Trim() to remove whitespaces of a string.
If it was a longer time since last trim coding I write:

string s = " text ";
s.Trim();

and be surprised why s is not changed. I need to write:

string s = " text ";
s = s.Trim();

Why are some string methods designed in this (not very intuitive) way? Is there something special with strings?

Upvotes: 5

Views: 2970

Answers (4)

JotaBe
JotaBe

Reputation: 39014

s.Trim() creates a new trimmed version of the original string and returns it instead of storing the new version in s. So, what you have to do is to store the trimmed instance in your variable:

  s = s.Trim();

This pattern is followed in all the string methods and extension methods.

The fact that string is immutable doesn't have to do with the decision to use this pattern, but with the fact of how strings are kept in memory. This methods could have been designed to create the new modified string instance in memory and point the variable to the new instance.

It's also good to remember that if you need to make lots of modifications to a string, it's much better to use an StringBuilder, which behaves like a "mutable" string, and it's much more eficient doing this kind of operations.

Upvotes: 7

Sandeep
Sandeep

Reputation: 7334

In addition to all the good answers, I also feel that the reason being Threadsaftey.

Lets say

string s = " any text "; s.Trim();

When you say this there is nothing stopping the other thread from modifying s. If the same string is modified, lets say the other thread remove 'a' from s, then what is the result of s.Trim()?

But when it returns the new string, though it is being modified by the other thread, the trim can make a local copy modify it and return modified string.

Upvotes: 1

gliderkite
gliderkite

Reputation: 8928

As it is written in MSDN Library:

A String object is called immutable (read-only), because its value cannot be modified after it has been created. Methods that appear to modify a String object actually return a new String object that contains the modification.

Because strings are immutable, string manipulation routines that perform repeated additions or deletions to what appears to be a single string can exact a significant performance penalty.

See this link.

Upvotes: 2

Tudor
Tudor

Reputation: 62439

Strings are immutable. Any string operation generates a new string without changing the original string.

From MSDN:

Strings are immutable--the contents of a string object cannot be changed after the object is created, although the syntax makes it appear as if you can do this.

Upvotes: 24

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