String.Replace on null values

Question

I have a Replace method which can accept Xml node names as variables, the Replace will be evaluated on each row in the Xml getting the value of the node before it evaluates the expression. Therefore if some nodes don't exist the Replace will be evaluating on a null.

Given this condition is the following code is justified?

<chocolates>
    <chocolate>
        <name>Mars Bar</name>
    </chocolate>
    <chocolate>
        <name>Bounty</name>
        <type>Coconut</type>
    </chocolate>
</chocolates>

Replace(type, 'C', 'c')

public string Replace(string a, string b, string c) 
{
    if (a == null) return null;
    if (b == null || c == null) return a;

    return a.Replace(b, c); 
}

If you gave the parameters better names it'd be easier to see what's going on — Mikey Mouse
– Mikey Mouse, Commented Apr 3, 2014 at 15:11

Dmitrii Bychenko · Accepted Answer · 2014-04-03 17:27:12Z

2

The code can be simplified:

// When designing public methods you'd rather give to the parameters more
// descriptive names than "a", "b", "c", e.g.
// "source", "toFind", "toReplace"
public string Replace(string a, string b, string c) 
{
    if ((a == null) || (b == null) || (c == null))
      return a;

    return a.Replace(b, c); 
}

Or even further with a help of the trenary operator:

public string Replace(string a, string b, string c) 
{
    return ((a == null) || (b == null) || (c == null)) ? a : a.Replace(b, c);
}

You should use String, e.g. "c", "C" not Char 'C', 'c' on call:

// All three arguments should be strings
String type = ...
...
Replace(type, "C", "c");

edited Apr 3, 2014 at 17:27

answered Apr 3, 2014 at 15:13

Dmitrii Bychenko

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Comments

Flo · Accepted Answer · 2014-04-03 15:14:09Z

0

Maybe you should call your function by :

Replace(type,"C","C");

(ofcourse "type" also needs to be a string value)

or try this to compare string to null :

if(a.Equals(null)) return null;

answered Apr 3, 2014 at 15:14

Flo

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Comments

Jaroslav Kubacek · Accepted Answer · 2014-04-03 15:23:11Z

0

You need also to check that b is not empty. Otherwise argument exception will occure

Console.WriteLine(Replace("dsfa", "", ""));
// Define other methods and classes here
public string Replace(string a, string b, string c) 
{
    if (a == null) return null; 
    if (String.IsNullOrEmpty(b) || c == null) return a;

    return a.Replace(b, c); 
}

answered Apr 3, 2014 at 15:23

Jaroslav Kubacek

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Comments

Mikey Mouse · Accepted Answer · 2014-04-03 15:30:30Z

0

An extension method would look neater I think

    public static class MyTestClass
    {
      public static string MyReplace(this string stringToSearch, string find, string replaceWith)
      {
        if(stringToSearch == null) return null;
        if(string.IsNullOrEmpty(find) || replaceWith == null) return stringToSearch;
        return stringToSearch.Replace(find, replaceWith);
      }
    }

Then you could just call

      type.MyReplace('C','c');

Edit: Added the full code for an extension class, and added isNullOrEmpty instead of just a null check for "find" as you don't wanna pass an empty string to the Replace call

edited Apr 3, 2014 at 15:30

answered Apr 3, 2014 at 15:17

Mikey Mouse

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