问题
In my method, I declare some variables, including int blockCount;. I call this method more than once. Using the Xcode debugger, I found out that after the second time the method was called, the value of blockCount was set to 364265, while it was set to 2, just a few milliseconds earlier.
It's not a real problem, since I can just set it to 0 or any other number I'd like, but is it bad programming habit to have a certain variable declared over and over again? I'm quite new to programming, and I want to make sure I'm doing things the right way. :)
回答1:
If you declare a variable but don't provide a value for it, it is considered "uninitialized". An uninitialized variable in C has an "undefined" value -- it's usually garbage, containing whatever happened to be at that address the last time something was written there. Strictly speaking, though, "undefined" means that you should under no circumstances try to use that value. (If you do a search for "nasal demons" this will be explained in quite colorful, and also useful, terms.*)
This variable, being local, is recreated every time the method runs, and thus gets a new actual, though still technically undefined value each pass.
It's generally recommended to not leave variables uninitialized, because the "random" value can cause bugs that are hard to find, and occasionally summon the aforementioned nasal demons. You're not doing anything wrong, but if you're not setting the actual value within a line or two of the declaration, I'd suggest initializing it to 0 or some sensible default:
int blockCount = 0;
*See also: What happens to a declared, uninitialized variable in C? Does it have a value?
来源：https://stackoverflow.com/questions/9726817/can-variables-be-set-randomly-when-declaring-them-again