CODEWITHSUNDEEP
c#
Joseph Izang
Joseph Izang

Reputation: 755

Variable Scope Confusion C#

I have a question on scope.

Why can I not return d and not access c? 

public string Test(string t)
{
    var x = someoutcome();

    //test to be sure of outcome
    if(x != null)
    {
        var b = "A string to be returned" + t;
        var c = anothermethod();
        if(typeof(c) == string)
        {
            var d = "Hurray c and b are strings" + b;
        }
    }
    return d;
}

Upvotes: 0

Views: 106

Answers (6)

Nicolas C
Nicolas C

Reputation: 235

yes the problem is really the scope of var d. After the } just after var d the variable doesn't exist anymore and you try to return it. This will rise an exception.

  1. first option

May be you need to declare var d at the same level as var x, it will be accessible in the if(x != null){...} loop. And you need to give it a default value, because if you wan't to return d and if x == Null??? you will have to anticipate it, d will be null, you cannot return null;

  1. second option

you return d in the loop if(x != null){...} and after }you return a default value like this:

public string Test(string t)
{
    var x = someoutcome();

    //test to be sure of outcome
    if(x != null)
    {
        var b = "A string to be returned" + t;
        var c = anothermethod();
        if(typeof(c) == string)
        {
            var d = "Hurray c and b are strings" + b;
            return d;//d exist only in this loop, and is return, the method is stoped here
        }
    }
    return empty.string;//if the code can't return d (x==Null or typeof(c) != string)
}

Upvotes: 0

D J
D J

Reputation: 7018

Block declares the scope of variable start with { and ends with }

If you declare a variable within a block construct such as an If statement, that variable's scope is only until the end of the block. The lifetime is until the procedure ends

look at the scope of variables https://msdn.microsoft.com/en-us/library/ms973875.aspx

Upvotes: 0

Sinatr
Sinatr

Reputation: 22008

Other answers explain scope. Here is a fixed version of your code:

public string Test(string t)
{
    var x = someoutcome();
    // define d here to have it available for return at the end of method block
    // note: you have to provide default value to return in case one of following "if" conditions are not true
    string d == null;
    if(x != null)
    {
        var b = "A string to be returned" + t;
        var c = anothermethod();
        if(c.GetType() == typeof(string))
            d = "Hurray c and b are strings" + b;
    }
    return d;
}

or simply (without defining d):

...
    if(c.GetType() == typeof(string))
        return "Hurray c and b are strings" + b;
}
return null;

Upvotes: 0

Fabjan
Fabjan

Reputation: 13676

Why i cannot return d

Reference to 'd' exists only in your if block and is lost when it finishes.

Why i cannot access c?

This is whole of a different story. The typeof operator is used to obtain the System.Type object and expects a type as parameter and not variable or reference to an instance of a type. Your 'c' is just a variable that holds a reference to type String. Change typeof(c) to typeof(String) or c.GetType() and you'll see that it works now

Upvotes: 0

bot_insane
bot_insane

Reputation: 2604

C# Spec, Section 3.7

The scope of a local variable declared in a local-variable-declaration is the block in which the declaration occurs.

What does it mean ?

Scope of d variable is starting from here:

if(typeof(c) == string)
{

and end with }. This is called block. Your variable d-s scope is block of mentioned if.

Upvotes: 3

Waescher
Waescher

Reputation: 5747

You're accessing c in the correct scope, I see no error here. The reason why you cannot return d is quite obvious: it is defined in an scope which does not include return d.

public string Test(string t)
{
    var x = someoutcome();

    //test to be sure of outcome
    if(x != null)
    {
        var b = "A string to be returned" + t;
        var c = anothermethod();
        if(typeof(c) == string)
        {
            var d = "Hurray c and b are strings" + b;
        } // ** FROM HERE ON, d WONT BE ACCESSIBLE ANYMORE **
    }  // ** FROM HERE ON, b & c WONT BE ACCESSIBLE ANYMORE **
    return d;
}

But you could return d directly instead of writing it in an variable:

public string Test(string t)
{
    var x = someoutcome();

    //test to be sure of outcome
    if(x != null)
    {
        var b = "A string to be returned" + t;
        var c = anothermethod();
        if(typeof(c) == string)
        {
            return "Hurray c and b are strings" + b;
        }
    }
    return string.Empty;
}

Please have a look at this site to read more about variables in scopes.

Upvotes: 0

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