I have a function that does a lot of finding and replacing on strings, using Regex and other string processing functions. Essentially I'm looping through a string, and adding the resulting data into a StringBuilder so its faster than modifying the string itself. Is there a faster way?
Essentially I'm looping through a string, and adding the resulting
data into a StringBuilder so its faster than modifying the string
itself. Is there a faster way?
StringBuilder class is faster when you want to concatenate some strings into a loop.
If you're concatening an array String.Concat() is faster bacause it has some overloads which accept arrays.
else use simply the + operator if you have to do something like: string s = "text1" + "text2" + "text3"; or use String.Concat("text1", "text2", "text3");.
For more info look here: Concatenate String Efficiently.
EDIT :
The + operator compiles to a call to String.Concat() as said usr in his comment.
Related
Really???
I've searched through https://msdn.microsoft.com/en-us/library/system.string(v=vs.110).aspx and don't see any method that can directly push a character onto the end of a string. The best I can figure is
mystr.Insert(mystr.Length, newchar.ToString());
which seems innefficient because of the overhead involved in converting the character to a string and performing string concatenation. My particular use case looks like
while (eqtn[curidx] >= '0' && eqtn[curidx] <= '9') istr.Insert(istr.Length, eqtn[curidx++].ToString());
only because I can't think of a better way to do it. Is there a better way?
Strings in .NET are immutable, so your code doesn't do anything. Every method on a String creates a new instance, it doesn't modify the existing string.
String class overrides + operator to create a new string with the character appended to the end:
istr = istr + eqtn[curidx++];
If you are doing a lot of such operations it will be more efficient to use a StringBuilder. It's basically a mutable String.
You can use the Append method to add a char to end. When you're ready, call ToString to get the constructed string.
Yes, that is absolutely right: you cannot push a character onto the end of a string because C# strings are immutable. Once you have an object, you are stuck with its value until you create a new string object.
On the other hand, creating a new string with an extra character at the end is very simple: use + operator overload that performs concatenation:
string s = "abc";
s += '9'; // s becomes "abc9"
Note that this solution is not so good for use in a loop, because if your loop runs N times you create N throw-away objects in the process. A better solution is to use StringBuilder, which provides a mutable string in C#. StringBuilder class has a convenient Append method, which pushes characters to the end of the StringBuilder. Once you are done building the string, call ToString to harvest the result as an immutable string object.
Trying to determine if it's a better practice to use string.Format in place of concatenating strings and if so, why is this? Also, are their advantages/disadvantages to one or the other that I should be aware of?
This:
string foo = "I" + " am " + " a " + " string.";
or:
string bar = string.Format("{0} am a {1}.", "I", "string");
Obviously oversimplified examples, just wanting to be clear.
The "best practice" should be the thing that makes your code the most readable and maintanable. The performance difference between concatenating strings versus using string.Format versus using a StringBuilder is so small that it's essentially irrelevant.
Assuming the first method was not optimized at compile time, because strings are immutable it will create many intermediate strings. It'll work from left to right so there will first be "I am ", then "I am a ", and finally "I am a string." which is stored in foo.
String.format will not make intermediate strings. To my understanding it does all the manipulation in a char[] which is then made immutable by being made a String.
Is there a quick way to pack an array of strings to a string?
More specifically,I have an array of strings like this:
string[] Operators = {"+","-","x","/"} and I would like to pack it to
string sOperators = "+-x/"
Of course, the obvious way is to read each item in the array and put it in the string individually, but is there a better way that people smarter than me can think of?
I have tried:
string sOperators="";
String.Join(sOperators,Operators);
Unfortunately, that won't work for me. Any thought?
Your code sample could just be incomplete but based on you've posted the problem is that you're not assigning the joined string anywhere. I think the following will do what you want;
string joined = String.Join(sOperators, Operators);
Join returns a new string, it does not make any changes to the arguments you pass it. You need to assign the return value to some field, property, constant, or variable in order to produce the desired result.
You can use String.Concat(Operators) (MSDN http://msdn.microsoft.com/en-us/library/k9c94ey1.aspx)
You can indeed use String.Join for this:
string sOperators = string.Join("", Operators);
I guess you just forgot to assign the result to a variable.
Is it possible to replace a substring in a string without assigning a return value?
I have a string:
string test = "Hello [REPLACE] world";
And I want to replace the substring [REPLACE] with something else:
test = test.replace("[REPLACE]", "test");
This works fine, but how can I do it without assigning the return value to a variable?
I want something like this:
test.replace("[REPLACE]", "test");
As mentioned by dlev, you can't do this with string as strings are immutable in .NET - once a string has been constructed, there's nothing you can do (excluding unsafe code or reflection) to change the contents. This makes strings generally easier to work with, as you don't need to worry about defensive copying, they're naturally thread-safe etc.
Its mutable cousin, however, is StringBuilder - which has a Replace method to perform an in-object replacement. For example:
string x = "Hello [first] [second] world";
StringBuilder builder = new StringBuilder(x);
builder.Replace("[first]", "1st");
builder.Replace("[second]", "2nd");
string y = builder.ToString(); // Value of y is "Hello 1st 2nd world"
You can't, because string is immutable. It was designed so that any "changes" to a string would actually result in the creation of a new string object. As such, if you don't assign the return value (which is the "updated" string, actually copy of the original string with applied changes), you have effectively discarded the changes you wanted to make.
If you wanted to make in-place changes, you could in theory work directly with a char[] (array of characters), but that is dangerous, and should be avoided.
Another option (as pointed out by Mr. Skeet below) is to use StringBuilder and its Replace() method. That being said, simple replacements like the one you've shown are quite fast, so you may not want to bother with a StringBuilder unless you'll be doing so quite often.
Strings in .NET are immutable. They cannot be edited in-line.
The closest you can get to in-line editing is to create a StringBuilder from a string. In-line fiddles with its contents and then get it to spit a string back out again.
But this will still produce a new string rather than altering the original. It is a useful technique, though, to avoid generating lots of intermediary strings when doing lots of string fiddling, e.g. in a loop.
You can't. You have to assign the value, as strings are immutable.
Built-in reference types (C# reference)
You can't. Strings are immutable in .NET.
You can't, as in C# strings are immutable. Something like this would violate that.
You need to have the return type of string, because the one you're working with cannot change.
Here is the code to fetch a string from HTML content and pass it to StringBuilder and set the value from your variable. You cannot do string.replace. You have to use StringBuilder while manipulating. Here in the HTML page I added [Name] which is replaced by Name from code behind. Make sure [Name] is unique or you can give any unique name.
string Name = txtname.Text;
string contents = File.ReadAllText(Server.MapPath("~/Admin/invoice.html"));
StringBuilder builder = new StringBuilder(contents);
builder.Replace("[Name]", Name);
StringReader sr = new StringReader(builder.ToString());
I have strings like this:
var abc = "text1 text2 text3";
I want to change "text3" to "textabc" in the string. Is there a way that I can do this without creating a new string?
Strings are immutable in C# so any operation inherently creates a new 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.
StringBuilders are often the most efficient way to perform manipulation on a "string" due to this fact. Especially if you are concatenating one char at a time for example.
See the StringBuilder.Replace() method - This does not require you reassign the result to another StringBuilder as it actually changes the StringBuilder itself.
Have a look at this article by the very famous Jon Skeet (you'll get to recongise him:)) all about using StringBuilder sensibly.
No, because strings are immutable, but you can reassign the new string to the same variable
var abc = "text1 text2 text3"
abc = abc.Replace("text3", "textabc");
string newString = abc.Replace("text3", "textabc");
Strings are immutables in the CLR : you can never ever change them.
The main question is what do you mean by writing "without creating a new string".
As stated, strings are immutable in .NET, that is, once they're created, they can't change.
However, you can replace them with a new string instance:
var abc = "text1 text2 text3";
abc = abc.Replace("text3", "textabc");
If you want more flexibility, you may want to use StringBuilder, in which you can remove and replace strings as much as you want, and finally use its ToString method to have the result as a string instance.