In C#, why is a variable not definitely assigned at the beginning of a finally block?
c#, try-catch
Solution
Simple reason is - There is no guarantee that the code in `try` or `catch` block will ever execute, before `finally` block.
`ThreadAbort` Exception can happen inside the `try` block, but before assignment executes.
Runtime code executes after exception is thrown but before code in `catch` blocks executes (Search for how exception handling works in .Net or "Structured Exception Handling").
Hence, code in try and catch block may never execute, before execution of `finally` block.
Problem
I don't understand why the following code produces an error. Normally I can figure things out from the language specification, but in this case I don't understand the language specification. This isn't causing problems in my code, by the way, I just want to understand the language. Example: ``` bool success; try { success = true; } catch { success = false; } finally { Console.WriteLine(success); // ERROR: Local variable 'success' might not be initialized before accessing } ``` This behavior appears to be true of all versions of C#, but the quotes below are from C# Language Specification 5.0. Section 5.3.3.14 Try-finally statements The definite assignment state of v at the beginning of finally-block is the same as the definite assignment state of v at the beginning of stmt. Here "beginning of stmt" refers to the beginning of the entire try-finally statement, i.e. just before `try`. Section 5.3.3.15 Try-catch-finally statements The following example demonstrates how the different blocks of a try statement (§8.10) affect definite assignment. ``` static void F() { int i, j; try { goto LABEL; // neither i nor j definitely assigned i = 1; // i definitely assigned } catch { // neither i nor j definitely assigned i = 3; // i definitely assigned } finally { // neither i nor j definitely assigned j = 5; // j definitely assigned } // i and j definitely assigned LABEL:; // j definitely assigned } ``` Can anyone explain why `success` (in my example) or `i` (in the language spec example) are not definitely assigned at the beginning of the finally-block?