When exactly should a StringBuilder be used?

[gicio]

Hi!

 

I�m very interesting in when to use exactly the StringBuilder?

 

For example for something like this?:

 

String strTest1 = �This�;

String strTest2 = �Test�;

StringBuilder stbTest = new StringBuilder();

stbTest.Append(strTest1). Append(�is a �). Append(stbTest);

 

 

can someone provide some sample codes when to use a StringBuilder?

 

And can someone tell me his experience about the performance of a StringBuilder?

 

 

Regards,

 

 

gicio

[bri189a]

from what I understand is this, and someone please correct me if I'm wrong.

 

A lot of people (including myself) do things such as:

Console.WriteLine("The value of X = " + x.ToString() + "!")

 

Not a big problem there, but a more advanced application may have:

string ret;
for(int x=0;x<variable.Length;x++)
{
    ret += ";next value=" + variable + " and is " + boolVar.ToString();
}

Over a larger iteration this is much more work for the processor than having:

string ret;
for(int x=0;x<variable.Length;x++)
{
    ret.Append(";next value=" + variable + " and is " + boolVar.ToString();

}

 

now I heard that second hand, but it's something to think about if it's true.

[dynamic_sysop]

i posted you a reply on codeguru :) , basically saying this ...

the easiest way to explain is , if you ever used vb6 , there might have been times when you needed to dim a string like this ....

Dim strString As String * 256

to make it have a buffer at the start, well the StringBuilder does basically that. here's 2 examples of using the API " GetClassName " , one using the StringBuilder , the other using just normal strings, try them and see the difference

using the StringBuilder .....

[DllImport("user32.dll", EntryPoint="GetClassNameA")]
static extern int GetClassName (int hwnd, System.Text.StringBuilder lpClassName, int nMaxCount);

private void button1_Click(object sender, System.EventArgs e)
{
   System.Text.StringBuilder str=new System.Text.StringBuilder(256); // buffer of 256 chars.
   GetClassName(base.Handle.ToInt32(),str,str.Capacity);
   MessageBox.Show(str.ToString());
}

using just a string ....

[DllImport("user32.dll", EntryPoint="GetClassNameA")]
static extern int GetClassName (int hwnd, string lpClassName, int nMaxCount);

private void button1_Click(object sender, System.EventArgs e)
{
   string str=string.Empty;
   GetClassName(base.Handle.ToInt32(),str,256);
   MessageBox.Show(str);
}

you will notice the string version returns an empty messagebox.

[Abbacabba]

Additionally:

 

Every time you manipulate a STRING you are creating a NEW string editing a buffer and returning that value into the newly created string.

 

Stringbuilder keeps the same instace of the STRING and can edit its value.

 

If you are doing many edits to a string variable then StringBuilder is for you.

 

Psudo-codeish EXAMPLE:

 

PLACE TO USE STRING:

String X = "Hello" + name;

 

PLACE TO USE STRINGBUILDER:

StringBuilder X;

X = somevalue;

for(i=0; i < 10000; i++)

{

more = somefunction(i);

X += more;

}

[bri189a]

Abbacabba - So then my post was actually pretty acurate... wonders will never cease!

[laptop_01]

I typically use it when I want to build a long, long string that will eventually ends up in a file.

 

Instead of writing to the file line by line, I create a stringBuilder, stuff it with my lines, and then write once.

[Grimfort]

Stringbuilders only have any speed usage when concatenating many thousands of strings. If you anywhere near 1000 id say use a stringbuilder, otherwise just use the normal & keyword. (making a new stringbuilder class takes more time then concat with a few &s)

 

For me the main use is building up data (for files) before throwing them out to disk, or over the network/internet. Often used in a for or loop statement they speed up your processing no end, if you work with data concat like I do, its worth moving over to .net just to use the stringbuilder.

 

e.g

 

       Dim strBuilder As StringBuilder = New StringBuilder()

       For intIndex = 0 To UBound(gMask)
            strBuilder.Append(gMask(intIndex))
       Next
  
       'Go save to disk (using strBuilder.ToString)

[Robby]

Yeah, for a handful of concatenated lines it's not worth using the builder.