C＃本地复制的变量值不断变化

Question

I am facing this strange problem with strings.

I assigned a string like this:

string temp = DateTime.UtcNow.ToString("s");
_snapShotTime = string.Copy(temp);

//here threads started....
//while thread progressing I am passing  _snapShotTime to create a directory.
//same in second threads.

But the time of local private variable _snapShotTime is keep on changing. I don't know why. I have used a local variable and copy value in it.

Thanks

Answer 1

I suspect your thread uses a lambda expression (or anonymous function) which captures _snapShotTime . That would indeed allow it to be changed. It's hard to say for sure without any code though.

If this is the problem, it's typically that you're referring to a captured variable which is declared outside the loop, but changed on every iteration of a loop. You can fix this by declaring a new variable which takes a copy of the original variable inside the loop, and only using that copy variable in the lambda expression. You'll get a "new" variable inside the loop on each iteration, so you won't have problems.

Answer 2

Why don't you just do

_snapShotTime = DateTime.UtcNow.ToString("s");

Also, place a breakpoint on that line and see when it is being called.

When it does break, see the stack and it will clarify things.

I suspect that your threads change the value of _snapShotTime

Answer 3

Strings are immutable, they do not change unless a variable is reassigned to a new string.

We need to see more code in order to help pinpoint the problem.