Windows salad: implementation principle of File Association

When you double-click a file in Windows, if a program is associated with the file extension, the associated program is used to open the file. How is it implemented internally? I will give you a brief introduction today.

Everything is in the Registry

All registered extensions are in the Windows registry and their key values are located:

HKEY_CLASSES_ROOT

For example, you can see that there are many registry key values:

Let's dig down the key value of .txt:

It is strange that no program is found to open the key value.

OSS is on the default value of. txt. Please refer to the default value of. txt:

The default value of. txt is:

Txtfile

So what is this txtfile? In fact, txtfile is also a key value located under HKEY_CLASSES_ROOT. Its path is:

HKEY_CLASSES_ROOT \ txtfile

Let's take a look at what txtfile is:

No. Here is a sub-entry of shell \ open \ command. open this entry again to see:

As you can see, notepad.exe is "Notepad", and % 1 is generally used to pass the opened file path.

I find this and I guess this is the default program to open.

Practice Verification

The above is a conjecture. You still need to verify it.

I created a new. test extension and registered this type as testfile.

Create another testfile entry:

Test:

Summary

First, in Windows, check whether the corresponding extension has been registered in the registry. If there is a registration, read the file type corresponding to the extension, find the file type, and then read the associated program from it, to open the program.

Source: Greenerycn