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Xiaobian to share with you about the use of hook functions, I believe that most people do not know much about it, so share this article for your reference, I hope you can learn a lot after reading this article, let's go to understand it!

The hook function is part of the Windows message handling mechanism. By setting the hook, the application can filter all messages and events at the system level and access messages that are inaccessible under normal circumstances. The essence of a hook is a program that handles system messages and hangs it into the system through system calls.

Hook function action

The interface that pops up about the hook function after a certain operation

The interface that pops up about the hook function after a certain operation

The hook function of WINDOWS can be considered one of the main features of WINDOWS. With them, you can capture events that occur in your own process or other processes. With hook, you can give WINDOWS a callback function that handles or filters events, also known as a "hook function," which WINDOWS calls every time an event of interest to you occurs.

Hook function type

There are two types of hooks: local and remote.

Local hooks hook only events of your own process.

Remote hooks can also hook events that occur in other processes.

There are two more remote hooks:

There are two kinds of hooks, system-level global hooks and thread-level hooks. Global hook functions need to be defined in DLL, and thread-level hooks are relatively simple at the beginning.

Actually, there are only three hook functions:

Set hook: SetWindowsHookEx

Release hook: UnhookWindowsHookEx

Continue with the hook: CallNextHookEx

The GetCurrentThreadID function is often used in thread-level hooks to get the ID of the current thread [1]

Brief introduction

System-wide will capture event messages that will happen to all processes in the system. When you create a hook, WINDOWS first creates a data structure in memory that contains information about the hook, and then adds the structure to the existing hook linked list. The new hook will be added in front of the old one. When an event occurs, if you install a local hook, the hook function in your process will be called. If it is a remote hook, the system must insert the hook function into the address space of other processes, which requires that the hook function be in a dynamic link library, so if you want to use a remote hook, you must put the hook function into the dynamic link library.

Special case

Of course, there are two exceptions: the work log hook and the work log playback hook. The hook function for these two hooks must be in the thread where the hook is installed. The reason is that these two hooks are used to monitor lower-level hardware events, and since they are recorded and played back, all events are of course in order. So if you put the callback function in DLL, the input events are recorded in several threads, so there is no guarantee that you will get the correct order.

These are all the contents of the article "what's the use of Hook functions?" Thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!

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