---
title: "Implement callbacks"
url: "https://docs.adyen.com/point-of-sale/classic-library-deprecation/classic-library-integrations/c-library-integration/calls-and-callbacks-c-library/implement-callbacks"
source_url: "https://docs.adyen.com/point-of-sale/classic-library-deprecation/classic-library-integrations/c-library-integration/calls-and-callbacks-c-library/implement-callbacks.md"
canonical: "https://docs.adyen.com/point-of-sale/classic-library-deprecation/classic-library-integrations/c-library-integration/calls-and-callbacks-c-library/implement-callbacks"
last_modified: "2026-05-23T12:56:20+02:00"
language: "en"
---

# Implement callbacks

[View source](/point-of-sale/classic-library-deprecation/classic-library-integrations/c-library-integration/calls-and-callbacks-c-library/implement-callbacks.md)

## About this task

In the C Library integration, you will implement most callbacks based on a defined signature. 

This includes:

* `initialization_CB`
* `library_shutdown_CB`
* `register_pos_CB`
* `register_ped_CB`
* `create_new_tender_CB`
* `library_exception_CB`
* `cancel_or_refund_CB`
* `show_screen_CB`
* `tx_store_CB`

We have defined a signature for each callback. The signature we provide looks like:

```
void initialization_CB(void * result, void * echo_pointer);
```

You will need to implement callback functions with the same signature. 

The process differs for callbacks that are added to the  `register_device_request` structure and passed with the `register_ped` call.  For these callbacks, see .

## Steps

To use these callbacks:

1. Implement the callback with the same signature. In the following example we will implement the `intitialization_CB` callback.

   ```cpp
   void initialization_CB(void * result, void * echo_struct){

       app_context_t * sPOS = (app_context_t *)echo_struct;

       sPOS->pending_callback = 0;      //mark handled

   }
   ```

2. Pass `intitialization_CB` as a parameter of the `init_library` call.

   ```
   ADYLibraryResult result = init_library(initReq, initialization_CB, sPOS);
   ```