A string assignment efficiency question

[Rawblues]

Teaching myself VB .NET, and the solution to this one is not obvious to me, but you guys can probably answer it pronto.

I've got a string of several thousand bytes in length, and I want to be able to replace characters anywhere within the string by absolute position. I'll always be replacing characters by exactly the same number of characters so methods to remove/insert etc are not appropriate.

i.e.

(lots of bytes..).........abcdefg.........(..lots of bytes)
becomes
(lots of bytes..).........abxyzfg.........(..lots of bytes)

I am going to want to do it thousands of times, so I want a solution that's very efficient, just altering the values of existing bytes in memory without any reallocation etc

What are my options?

 

[jmcilhinney]

Using an actual String object would be the least efficient way. Using a StringBuilder object would be more efficient. If you aren't changing the number of characters then you could also convert to a Char array and alter individual Char objects. The most efficient would be to write a DLL in C# and use unsafe code, which supports pointers. I believe that you may be able to get at the memory directly using the Marshal class, but I can't tell you the details. I'm sure if it's possible then it's messy as VB was never really designed for things particularly low-level.

 

[gazeranco]

Just for my own dumb curiosity, Why would you need to do this? what does it all mean

 

[Rawblues]

Thanks

..to jmcilhinney

Your answer confirms that I wasn't being totally stupid, then. I'll try the char array approach and see how that goes. Looks like the C# route might be more flexible for real life situations...

..to gazeranco

This is the kind of thing that you often want to be able to do. When I coded up the obvious solution to my problem using string concatenation etc, the performance was so crap as to be unusable (on a 2.6GHz m/c + 512Mb RAM), hence the question.