Is there anything similar to PHP isset() in C#?

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Hi There,

I come from a PHP background and would like to know if there's a way to check if a variable exists, and if not create it.

Something similar as seen in the the PHP code below.

if(isset($variable)){
    echo 'variable is set';
}else{
    echo 'variable is not set';
    $variable = 'This variable is now set';
}

Currently I am getting the error "Cannot use local variable 'pricelist' before it is declared". Keep in mind this is a C# console application, not a web based app.

Regards,

What I have tried:

Online research but could not find anything unfortunately.

Posted 21-Mar-17 21:59pm

Zach West

Updated 21-Mar-17 22:22pm

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Tomas Takac · Accepted Answer · 2017-03-21T22:22:00

In C# all variables must be declared before they are used:

C#

string variable = null; // <- declaration
if(variable != null)
{
    Console.WriteLine("variable is set");
}
else
{
    Console.WriteLine("variable is not set");
    variable = "This variable is now set";
}

But the previous example is a bit silly. Let's assume you have a method and you want to test an argument:

C#

public void Run(string variable)
{
    if(variable != null)
    {
        Console.WriteLine("variable is set");
    }
    else
    {
        Console.WriteLine("variable is not set");
    }
}

In any case the variable must exist before you first use it. And C# forces you to initialize all local variables explicitly. On the other hand member fields of a class get default values assigned so this will work:

C#

class Test
{
    private string variable;
    
    public void Run()
    {
        if(variable != null)
        {
            Console.WriteLine("variable is set");
        }
        else
        {
            Console.WriteLine("variable is not set");
            variable = "This variable is now set";
        }
    }
}