Compiler Error CS0165
Use of unassigned local variable 'name'
The C# compiler does not allow the use of uninitialized variables. If the compiler detects the use of a variable that might not have been initialized, it generates CS0165. For more information, see Fields (C# Programming Guide). Note that this error is generated when the compiler encounters a construct that might result in the use of an unassigned variable, even if your particular code does not. This avoids the necessity of overly-complex rules for definite assignment.
For more information, see https://blogs.msdn.com/ericlippert/archive/2006/08/18/706398.aspx.
Example
The following sample generates CS0165:
// CS0165.cs
using System;
class MyClass
{
public int i;
}
class MyClass2
{
public static void Main(string [] args)
{
int i, j;
if (args[0] == "test")
{
i = 0;
}
/*
// to resolve, either initialize the variables when declared
// or provide for logic to initialize them, as follows:
else
{
i = 1;
}
*/
j = i; // CS0165, i might be uninitialized
MyClass myClass;
myClass.i = 0; // CS0165
// use new as follows
// MyClass myClass = new MyClass();
// myClass.i = 0;
}
}
The following code produces CS0165 in Visual Studio 2008 but not in Visual Studio 2005:
//cs0165_2.cs
class Program
{
public static int Main()
{
int i1, i2, i3, i4, i5;
// this is an error, because 'as' is an operator
// that is not permitted in a constant expression.
if (null as object == null)
i1 = 1;
// this is an error, because 'is' is an operator that
// is not permitted in a constant expression.
// warning CS0184: The given expression is never of the provided ('object') type
if (!(null is object))
i2 = 1;
// this is an error, because a variable j3 is not
// permitted in a constant expression.
int j3 = 0;
if ((0 == j3 * 0) && (0 == 0 * j3))
i3 = 1;
// this is an error, because a variable j4 is not
// permitted in a constant expression.
int j4 = 0;
if ((0 == (j4 & 0)) && (0 == (0 & j4)))
i4 = 1;
// this might be an error, because a variable j5 is not
// permitted in a constant expression.
// warning CS1718: Comparison made to same variable; did you mean to compare something else?
int? j5 = 1;
if (j5 == j5)
i5 = 1;
System.Console.WriteLine("{0}{1}{2}{3}{4}{5}", i1, i2, i3, i4, i5); //CS0165
return 1;
}
}
This error occurs in recursive delegate definitions and can be avoided by defining the delegate in two statements:
class Program
{
delegate void Del();
static void Main(string[] args)
{
Del d = delegate() { System.Console.WriteLine(d); }; //CS0165
// Try this instead:
// Del d = null;
//d = delegate() { System.Console.WriteLine(d); };
d();
}
}
Change History
Date |
History |
Reason |
---|---|---|
July 2008 |
Added text and code example for recursive delegates. |
Content bug fix. |