Do you have to initialize a string variable inside a method?

Question

I am programming in C# and I keep getting an error for my string variable result.

When I hover over the line return result it says use of unassigned local variable.

Do I have to assign result a value before I use it? How come i do not get the same error for SqlDataReader reader?

string searchbyLastName(string lastname) { string result; SqlDataReader reader; try { reader = myCommand.ExecuteReader(); if (reader.HasRows) { while (reader.Read()) { if (reader["LastName"].ToString() == lastname) { result = reader.GetString(0); break; } } return result; } else return "No results found"; } catch (Exception) { return("Database Error"); } }

Ed Swangren · Accepted Answer · 2014-10-03 03:43:38Z

3

if (reader["LastName"].ToString() == lastname)

If that is never true then result is not initialized. The SqlDataReader is always initialized prior to being used. Just initialize the string.

var result = "";

answered Oct 3, 2014 at 3:43

Ed Swangren

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7 Comments

Dan Hunex Over a year ago

Bad practice. Use var result = String.Empty;

Ed Swangren Over a year ago

@DanHunex: No thank you, please explain why you consider it a "bad practice". There hasn't been any actual semantic difference in quite some time due to string interning. Do you simply enjoy typing?

Dan Hunex Over a year ago

Why do you think String.IsNullOrWhitespace is added? Because people sometimes write " " instead of "" . But String.Empty always guarantee that it is empty

Ed Swangren Over a year ago

@DanHunex: They do? Weird. I have never, in over a decade of work, seen that error. I think I'll stick with "", thanks though. PS: IsNullOrWhitespace was almost certainly not added to account for typos when attempting to initialize a variable to an empty string. It's meant to check for empty input, not incorrectly initialized variables.

Dan Hunex Over a year ago

Well, you can also see this but i m not trying to convince you with more than 10 years of experience stackoverflow.com/questions/2905378/string-empty-versus

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Hans Keﬆing · Accepted Answer · 2014-10-03 07:47:55Z

The compiler needs to know you have definitely assigned a value to a variable, at the point where you are using that value.

In your case reader is always assigned a value (reader = myCommand.ExecuteReader();), but result isn't, because that depends on reader["LastName"].ToString() == lastname being true, which may never happen (even if you designed the system so that in reality you always find a match - the compiler doen't know that).

So somewhere before you enter that while-loop you have to assign a value. result = null would be enough. This value could also be used to signal a "lastname not found" condition to the calling code.

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