CODEWITHSUNDEEP
c#string
omega
omega

Reputation: 43863

How slow is passing large strings as return values in C#?

I want to know how return values for strings works for strings in C#. In one of my functions, I generate html code and the string is really huge, I then return it from the function, and then insert it into the page. But I want to know should I pass a huge string as a return value, or just insert it into the page from the same function?

When C# returns a string, does it create a new string from the old one, and return that?

Thanks.

Upvotes: 4

Views: 1734

Answers (3)

NPSF3000
NPSF3000

Reputation: 2451

Returning a string is a cheap operation - as mentioned it's purely a matter of returning 32 or 64 bits (4 or 8 bytes).

However, as Sten Petrov points out string + operations involve the creation of a new string, and can be a little expensive. If you wanted to save performance & memory I'd suggest doing something like this:

static int i = 0;
static void Main(string[] args)
{
    while (Console.ReadLine() == "")
    {

        var pageSB = new StringBuilder();

        foreach (var section in new[] { AddHeader(), AddContent(), AddFooter() })
            for (int i = 0; i < section.Length; i++)
                pageSB.Append(section[i]);

        Console.Write(pageSB.ToString());
    }

}

static StringBuilder AddHeader()
{
    return new StringBuilder().Append("Hi ").AppendLine("World");
}

static StringBuilder AddContent()
{
    return new StringBuilder()
        .AppendFormat("This page has been viewed: {0} times\n", ++i);
}

static StringBuilder AddFooter()
{
    return new StringBuilder().Append("Bye ").AppendLine("World");
}

Here we use the StringBuilders to hold a reference to all the strings we want to concat, and wait until the very end before joining them together. This'll save many unnecessary additions (which are memory and CPU heavy in comparison).

Of course, I doubt you'll actually see any need for this in practise - and if you do I'd spend some time learning about pooling etc. to help reduce the garbage created by all the string builders - and maybe consider creating a custom 'string holder' that suits your purposes better.

Upvotes: 1

Henk Holterman
Henk Holterman

Reputation: 273274

System.String is a reference type (class) and so passing as parameter and returning only involve the copying of a reference (32 or 64 bits).

The size of the string is not relevant.

Upvotes: 8

CSJ
CSJ

Reputation: 3941

Strings (or any other reference type) are not copied when returning from a function, only value types are.

Upvotes: 21

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