Convert.ToBoolean fails with "0" value

Question

I'm trying to convert the value "0" ( System.String ) to its Boolean representation, like:

var myValue = Convert.ToBoolean("0"); // throwing an exception here

I've looked at the MSDN page, and in the code-sample block, I found these lines:

ConvertToBoolean("0");
// ...
Unable to convert '0' to a Boolean.

In my code, I'm converting from the System.String to Boolean like this:

// will be OK, but ugly code
var myValue = Convert.ToBoolean(Convert.ToInt32("0"));

• Is there any other way to convert to the Boolean type with not such ugly code?
• Why does such an exception occur? Because of converting from the reference type System.String to the value type the System.Boolean, but System.Int32 is also a value type, isn't it?

Solution 1

This is happening because Convert.ToBoolean is expecting one of the following:

• "True" (String) = true
• "False" (String) = false
• 0 (numerical type; int, double, float, etc.) = false
• Any non-0 (numerical type; ...) = true
• null = false

Any other value is invalid for Boolean.

You've already got a clean approach:

var myValue = Convert.ToBoolean(Convert.ToInt32("0"));

---

Edit: You can create an extension method that will handle a few of these cases for you, while hiding away the ugliness of handling the conversion.

This extension provides a very loose interpretation of Boolean:

• "True" (String) = true
• "False" (String) = false
• "0" (String) = false
• Any other string = true

Code:

public static class Extensions
{
    public static Boolean ToBoolean(this string str)
    {
        String cleanValue = (str ?? "").Trim();
        if (String.Equals(cleanValue, "False", StringComparison.OrdinalIgnoreCase))
            return false;
        return
            (String.Equals(cleanValue, "True", StringComparison.OrdinalIgnoreCase)) ||
            (cleanValue != "0");
    }
}

---

Alternatively, if you want a more strict approach, which follows what the .NET Framework expects; then simply use try/catch statements:

public static class Extensions
{
    public static Boolean ToBoolean(this string str)
    {
        try
        {
            return Convert.ToBoolean(str);
        }
        catch { }
        try
        {
            return Convert.ToBoolean(Convert.ToInt32(str));
        }
        catch { }
        return false;
    }
}

Albeit, not a clean or pretty approach, but it guarantees more possibilities of getting the correct value. And, the Extensions class is tucked away from your data/business code.

In the end, your conversion code is relatively simple to use:

String myString = "1";
Boolean myBoolean = myString.ToBoolean();

Solution 2

public static class BooleanParser
{
    public static bool SafeParse(string value)
    {
        var s = (value ?? "").Trim().ToLower();
        return s == "true" || s == "1";
    }
}

---

static readonly HashSet<string> _booleanTrueStrings = new HashSet<string> { "true", "yes", "1" };
static readonly HashSet<string> _booleanFalseStrings = new HashSet<string> { "false", "no", "0" };

public static bool ToBoolean(string value)
{
    var v = value?.ToLower()?.Trim() ?? "";
    if (_booleanTrueStrings.Contains(v)) return true;
    if (_booleanFalseStrings.Contains(v)) return false;
    throw new ArgumentException("Unexpected Boolean Format");
}

Solution 3

Since it's really a matter of still doing those conversions and such, how about an extension method?

public static class Extensions {
    public static bool ToBool(this string s) {
        return s == "0" ? false : true;
    }
}

and so then you would use it like this:

"0".ToBool();

and now you could easily extend this method to handle even more cases if you wanted.

Solution 4

If you know that it would be an int then you can convert it to int then to bool. Following will try for conversion to bool by attempting the string then attempting with number.

public bool ToBoolean(string value)
{
  var boolValue = false;
  if (bool.TryParse(value, out boolValue ))
  {
    return boolValue;
  }

  var number = 0;
  int.TryParse(value, out number))
  return Convert.ToBoolean(number);
}

Solution 5

Fast enough and simple:

public static class Extensions
{
        static private List<string> trueSet = new List<string> { "true","1","yes","y" };

        public static Boolean ToBoolean(this string str)
        {
            try
            { return trueSet.Contains(str.ToLower()); }
            catch { return false; }
        }
}

View more solutions

Comments

[Paul Kearney - pk]

The example you reference is showing that there are invalid strings that the ToBoolean() method will reject. In addition to "0", they show examples of "TrueString" and string.Empty. The sample is showing that these are invalid, not that you can actually use those values.

[Bernhard]

why not use var res="1yestrue".Contains(yourVar)? There are also Boolean.Parse() / Boolean.TryParse() ?

[super cool]

simply use Convert.ToInt32("0") > 0 which gives you bool .

[Secret]

try to convert to the Boolean type the "0" as I said in the topic and look at the msdn sample on: msdn.microsoft.com/en-us/library/86hw82a3.aspx, you will get an excpetion with a try of converting the "0" string value.

[Jesse]

Because "0" is not "True" or "False". The only string representation accepted is "True" or "False".

[Secret]

you have refreshed you answer :) first variant of it was different and hold the "0" in the list, so my comment was referenced to it, not the refreshed one :) also the cleanest approach does look ugly for code-style

[Toan Vo]

You can use extension method to have the Parse Boolean as you wish. It will make your code clean and straight forward into convert boolean from string.

[Jesse]

@ToanVo Thanks for the tip; I've added some sample Extensions methods.

[Jesse]

@OlegOrlov Glad this answer helped!

[Secret]

@Jesse thank you too for the great answer ;) I think, that such a question will be a good exercise for the students or a good test for the job interview. Just to make a Q in the test about such a problem and ask about solutions or possible exceptions.