C# += (plus equals) (Assignment by addition) working very slow, when string is too long?

Question

I have a for loop and what I do is this.

forloop ( loop 7000 times)
{
x += 2000_char_long_string;
}

Code lasts really long time in this forloop, maybe more than 1 minute. How can I solve this problem?

Thanks.

Answer 1

Use a StringBuilder.

StringBuilder sb = new StringBuilder();
for(int i=0; i< 200; i++){
   sb.append(longString);
}
return sb.ToString();

When you use += on strings, you keep creating new strings, and keep locating larger and larger blocks of memory. That is why the operation is so slow.

Answer 2

Using a StringBuilder, as @Kobi referenced you can still increase performance by initializing it. It seems you can determine the final size of the string in advance.

StringBuilder sb = new StringBuilder(7000*2000);
for(int i=0; i< 7000; i++){
   sb.append(2000_char_long_string);
}
return sb.ToString();