Question

I want to check if a variable is initialized at run time, programmatically. To make the reasons for this less mysterious, please see the following incomplete code:

string s;

if (someCondition) s = someValue;
if (someOtherCondition) s = someOtherValue;

bool sIsUninitialized = /* assign value correctly */;

if (!sIsUninitialized) Console.WriteLine(s) else throw new Exception("Please initialize s.");

And complete the relevant bit.

One hacky solution is to initialize s with a default value:

string s = "zanzibar";

And then check if it changed:

bool sIsUninitialized = s == "zanzibar";

However, what if someValue or someOtherValue happen to be “zanzibar” as well? Then I have a bug. Any better way?

Answer 1

Code won’t even compile if the compiler knows a variable hasn’t been initialized.

string s;
if (condition) s = "test";
// compiler error here: use of unassigned local variable 's'
if (s == null) Console.Writeline("uninitialized");

In other cases you could use the default keyword if a variable may not have been initialized. For example, in the following case:

class X
{ 
    private string s;
    public void Y()
    {
        Console.WriteLine(s == default(string));  // this evaluates to true
    }
}

The documentation states that default(T) will give null for reference types, and 0 for value types. So as pointed out in the comments, this is really just the same as checking for null.

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This all obscures the fact that you should really initialize variables, to null or whatever, when they are first declared.