What is the major differences between Convert.ChangeType or Convert.ToInt32?

Question

Is there any performance benefits of one over another among Convert.ChangeType or Convert.ToInt32 or int.Parse

Answer 1

If you know you're going to be converting a string to Int32, using Convert.ChangeType seems an obscure way of doing that. I would definitely prefer either of the other calls to that.

The main difference between int.Parse and Convert.ToInt32(x) is that Convert.ToInt32(null) returns 0 where as int.Parse(null) will throw an exception. Of course, int.Parse also gives you more control in terms of what culture is used.

I very much doubt that there's any performance benefit of one over the other: I would expect Convert.ToInt32 to call int.Parse rather than the other way round - but it's not documented to work that way, and the hit of a single method call is unlikely to be significant. (It may well be inlined anyway.)

Answer 2

private const int maxValue = 1000000;
    static void Main(string[] args)
    {
        string[] strArray = new string[maxValue];
        for (int i = 0; i < maxValue; i++)
        {
            strArray[i] = i.ToString();
        }
        int[] parsedNums = new int[maxValue];
        CalcChangeTypePerf(strArray,parsedNums);
        CalcToInt32Perf(strArray, parsedNums);
        CalcIntParse(strArray, parsedNums);
    }
    public static void CalcChangeTypePerf(string[] strArray,int[] parsedArray)
    {
        Stopwatch stopwatch = new Stopwatch();
        stopwatch.Start();
        for (int i = 0; i < maxValue; i++)
        {
            parsedArray[i] = (int)Convert.ChangeType(strArray[i], typeof(int));
        }
        stopwatch.Stop();
        Console.WriteLine("{0} on CalcChangeTypePerf", stopwatch.ElapsedMilliseconds);
    }
    public static void CalcToInt32Perf(string[] strArray, int[] parsedArray)
    {
        Stopwatch stopwatch = new Stopwatch();
        stopwatch.Start();
        for (int i = 0; i < maxValue; i++)
        {
            parsedArray[i] = Convert.ToInt32(strArray[i]);
        }
        stopwatch.Stop();
        Console.WriteLine("{0} on CalcToInt32Perf", stopwatch.ElapsedMilliseconds);
    }
    public static void CalcIntParse(string[] strArray, int[] parsedArray)
    {
        Stopwatch stopwatch = new Stopwatch();
        stopwatch.Start();
        for (int i = 0; i < maxValue; i++)
        {
            parsedArray[i] = int.Parse(strArray[i]);
        }
        stopwatch.Stop();
        Console.WriteLine("{0} on CalcIntParse", stopwatch.ElapsedMilliseconds);
    }

This simple test results this

266 on CalcChangeTypePerf
167 on CalcToInt32Perf
165 on CalcIntParse