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String vs StringBuilder
Hi,
I'm creating a json string. I have some json encoders that receive objects and return json string. I want to assemble these strings into one long string.
What's the difference between using a string builder and declaring a string an appending strings to it.
Thanks.
When you append to a string, you are creating a new object each time you append, because strings are immutable in .NET.
When using a StringBuilder, you build up the string in a pre-allocated buffer.
That is, for each append to a normal string; you are creating a new object and copying all the characters into it. Because all the little (or big) temporary string objects eventually will need to get garbage-collected, appending a lot of strings together can be a performance problem. Therefore, it is generally a good idea to use a StringBuilder when dynamically appending a lot of strings.
string is immutable and you allocate new memory each time you append strings.
StringBuilder allows you to add characters to an object and when you need to use the string representation, you call ToString() on it.
StringBuilder works like string.format() and is more efficient than manually appending strings or +ing strings. Using + or manually appending creates multiple string objects in memory.
Copies. The stringbuilder doesn't make new copies of the strings every time; AFAIK Append just copies the bytes into a pre-allocated buffer most of the time rather than reallocating a new string. It is significantly faster! We use it at work all the time.
string.Format is using StringBuilders inside. Using StringBuilder is more optimal because you will work with it exactly as you need without the overhead that Format() needs to interpret all your args in your format string.
Imagine only that string.Format() needs to find all your "{N}" sequences in your formatting string... An extra job, huh?
Strings are immutable in C#. This makes appending strings a relatively expensive. StringBuilder solves this problem by creating a buffer and characters are added to the buffer and converted to string at the end of operation.
Look here for more info.
In the .NET Framework everytime you add another string to an existing string in creates a completely new instance of a string. (This takes up a lot of memory after a while)
StringBuilder uses a single instance even when you add more strings to it.
It has everything to do with performance.
String vs StringBuilder will help you understand the different between String and StringBuilder.
Related
Isn't a string already a character array in c#? Why is there a explicit ToCharacterArray function? I stumbled upon this when I was looking upon ways to reverse a string and saw a few answers converting the string to a character array first before proceeding with the loop to reverse the string. I am a beginner in coding.
Sorry if this seems stupid, but I didn't get the answer by googling.
Isn't a string already a character array in c# ?
The underlying implementation is, yes.
But you are not allowed to directly access that. String is using encapsulation to be an immutable object.
The actual array is private and hidden from view. You can use an indexer (property) to read characters but you cannot change them. The indexer is read only.
So yes, you do need ToCharacterArray() for reversing and similar actions. Note that you always end up with a different string, you cannot alter the original.
Isn't a string already a character array in c# ?
No, a string is a CLASS that encapsulates a "sequential collection of characters" (see Docs). Notice it doesn't explicitly say an "Array of Char". Now, it may be true that the string class currently uses a character array to accomplish this, but that doesn't mean it ~must~ use a character array to achieve that end. This is a fundamental concept of Object Oriented Programming that combines information hiding and the idea of a "black box" that does something. It doesn't matter how the black box (class) accomplishes its task under the hood, as long is it doesn't change the public interface presented to the end user. Perhaps, in the next version of .Net, some new-fangled magical structure that is not an array of characters will be used to implement the string class. The end user may not be aware that this change has even occurred because they can still use the string class in the same way, and if they so desire, could still output the characters to an array with ToCharArray()...even though internally the string is no longer an array of characters.
Yes String type is a character array but string array is not an character array you must have to convert each string in your array in char type so that you can easily reverse its indexes and then convert it into temporary string and then add that string to array to be reversed
Internally, the text is stored as a sequential read-only collection of Char objects.
See Programming Guide Docs
Console.WriteLine(StringHelper.ReverseString("framework"));
Console.WriteLine(StringHelper.ReverseString("samuel"));
Console.WriteLine(StringHelper.ReverseString("example string"));
OR
public static string ReverseString(string s)
{
char[] arr = s.ToCharArray();
Array.Reverse(arr);
return new string(arr);
}
It is 2019 and we have a banking project which uses mainframe as data store and transactions.
We are using DTO's (Commarea, plain c# class) that is converted to plain string (this is how mainframe works) then sent to Mainframe.
While converting a class to string representation we use several string operations such as substring, pad left, pad right, trim etc.
As you can imagine, this causes several string allocations and hence garbage collection. It is usually at generation 0 but still.
Especially types like Decimal which is a Pack type in mainframe that fits into 8 bytes creates several strings.
I tried using ReadonlySpan<char> for example for substring. See example.
However, there are operations like PadRight, PadLeft which is not avaiable, because it is a read only span.
Update:
To clarify a part of conversion happens as follows:
val.Trim().Substring(5).PadRight(10);
I know that this creates 3 string. I know strings are immutable. My question is about doing the above operation with ReadonlySpan or Memory.
I can not use ReadonlySpan only for substring because as soon as I call ToString method I m losing the benefits.
I have to call ToString all the way at the end.
Is there another construct that supports other operations behind substring, that I can actually add remove data to the memory?
Thanks.
Using ReadOnlySpan can help reduce the number of string allocations in your code, but it won't eliminate them completely. This is because ReadOnlySpan is a read-only view of a sequence of characters, so you cannot modify the underlying data using a ReadOnlySpan.
To avoid unnecessary string allocations, you can use the string.AsSpan() method to get a ReadOnlySpan view of a string, and then use the Span.Slice() method to get substrings without allocating new strings. For example, you could use the following code to get a substring of a string without allocating a new string:
string val = "Hello world";
ReadOnlySpan<char> span = val.AsSpan();
ReadOnlySpan<char> substring = span.Slice(5);
However, as mentioned earlier, you cannot use ReadOnlySpan to modify the underlying data, so you will still need to allocate new strings for operations like PadRight and PadLeft. To avoid these allocations, you can use a StringBuilder to build up the string piece by piece, and then call ToString() on the StringBuilder when you're done. This will allow you to perform string operations without allocating new strings for each operation.
In summary, using ReadOnlySpan can help reduce the number of string allocations in your code, but it won't eliminate them completely. To avoid allocating new strings for each string operation, you can use a StringBuilder to build up the final string piece by piece.
string val = "Hello world";
StringBuilder builder = new StringBuilder(val.Length);
// Trim the string
builder.Append(val.Trim());
// Get a substring starting at the 5th character
builder.Append(val, 5, val.Length - 5);
// Pad the string with spaces to the right, to make it 10 characters long
builder.PadRight(10, ' ');
// Convert the final string to a regular string
string result = builder.ToString();
Some text fields in my database have bad control characters embedded. I only noticed this when trying to serialize an object and get an xml error on char and . There are probably others.
How do I replace them using C#? I thought something like this would work:
text.Replace('\x2', ' ');
but it doesn't.
Any help appreciated.
Strings are immutable - you need to reassign:
text = text.Replace('\x2', ' ');
exactly as was said above, strings are immutable in C#. This means that the statement:
text.Replace('\x2', ' ');
returned the string you wanted,but didn't change the string you gave it. Since you didn't assign the return value anywhere, it was lost. That's why the statement above should fix the problem:
text = text.Replace('\x2', ' ');
If you have a string that you are frequently making changes to, you might look at the StringBuilder object, which works very much like regular strings, but they are mutable, and therefore much more efficient in some situatations.
Good luck!
-Craig
The larger problem you're dealing with is the XmlSerialization round trip problem. You start with a string, you serialize it to xml, and then you deserialize the xml to a string. One expects that this always results in a string that is equivalent to the first string, but if the string contains control characters, the deserialization throws an exception.
You can fix that by passing an XmlTextReader instead of a StreamReader to the Deserialize method. Set the XmlTextReader's Normalization property to false.
You should also be able to solve this problem by serializing the string as CDATA; see How do you serialize a string as CDATA using XmlSerializer? for more information.
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?
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.
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.
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.
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.
I'm building sitemaps and I need a way to quickly check how many UTF-8 encoded bbytes StringBuilder currently contains?
The naive way to do this would be to:
Encoding.UTF8.GetBytes(builder.ToString()).Length
But isn't this a bit bloated?
Using builder.Length doesn't work as certain charactes resolved to 2 bytes such as ÅÄÖ.
You could use this:
Encoding.UTF8.GetByteCount(builder.ToString());
Unfortunately, unlike Java where there is a CharSequence interface, you cannot directly process the StringBuilder without first converting it to a string.