CODEWITHSUNDEEP
c#.netpinvokefcl
Amirreza H
Amirreza H

Reputation: 63

How does .NET framework low level APIs work?

One of the questions that i always faced was the implementation of .NET Framework class libraries.

I know some of the methods original implementation:

For example : 

MessageBox.Show("...");

As i know this method must have used P/Invoke to call Win32 API.

but something like this:

System.Convert.ToInt32(mystr);

I actually don't know how it works because conversion between int and string is not possible in pure C#.(Can you do exact same thing without using that method? Actually I don't know).

Finally if you know the answer please clarify these concepts for me speicially the 2nd example.

Upvotes: 1

Views: 479

Answers (4)

Ani
Ani

Reputation: 113402

Microsoft has made the BCL available online at: http://referencesource.microsoft.com

Calling Convert.ToInt32(string) will eventually call int.Parse, which in turn will eventually call the actual routine on an internal Number class here:

One of the basic routines listed there is as follows:

    [System.Security.SecuritySafeCritical]  // auto-generated
    private unsafe static Boolean NumberToInt32(ref NumberBuffer number, ref Int32 value) {

        Int32 i = number.scale;
        if (i > Int32Precision || i < number.precision) {
            return false;
        }
        char * p = number.digits;
        Contract.Assert(p != null, "");
        Int32 n = 0;
        while (--i >= 0) {
            if ((UInt32)n > (0x7FFFFFFF / 10)) {
                return false;
            }
            n *= 10;
            if (*p != '\0') {
                n += (Int32)(*p++ - '0');
            }
        }
        if (number.sign) {
            n = -n;
            if (n > 0) {
                return false;
            }
        }
        else {
            if (n < 0) {
                return false;
            }
        }
        value = n;
        return true;
    }

Upvotes: 5

Frank
Frank

Reputation: 4481

Implementation of MessageBox.Show is here.

Implementation of Convert.ToString is here.

Upvotes: 1

Jon Skeet
Jon Skeet

Reputation: 1500515

Can you do exact same thing without using that method? Actually Nope.

You absolutely can. Here's a really inefficient way of doing it - which doesn't consider overflow, invalid input or negative numbers, but demonstrates the general principle.

int ParseStringToInt32(string text)
{
    int result = 0;
    foreach (char c in text)
    {
        result = result * 10 + (c - '0');
    }
    return result;
}

Fundamentally there's nothing mystical about the process of parsing a string as an Int32. It's just a case of looking at each character, considering its numeric value, and doing some arithmetic.

Indeed, there are times when it's worth doing it manually - in Noda Time we have our own numeric parsing code to allow a limited number of characters to be parsed without having to take a substring.

Upvotes: 6

ro-E
ro-E

Reputation: 299

try this: it's not the Microsoft implementation, since it's not open source. but it should give you an idea

https://github.com/mono/mono/blob/master/mcs/class/Managed.Windows.Forms/System.Windows.Forms/MessageBox.cs

Upvotes: 1

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