---
title: "Initialize the library"
url: "https://docs.adyen.com/point-of-sale/classic-library-deprecation/classic-library-integrations/c-library-integration/key-steps-c-library/initialize-the-library-c-library"
source_url: "https://docs.adyen.com/point-of-sale/classic-library-deprecation/classic-library-integrations/c-library-integration/key-steps-c-library/initialize-the-library-c-library.md"
canonical: "https://docs.adyen.com/point-of-sale/classic-library-deprecation/classic-library-integrations/c-library-integration/key-steps-c-library/initialize-the-library-c-library"
last_modified: "2026-05-23T12:56:20+02:00"
language: "en"
---

# Initialize the library

[View source](/point-of-sale/classic-library-deprecation/classic-library-integrations/c-library-integration/key-steps-c-library/initialize-the-library-c-library.md)

Before the library can be used, you must initialize it with the `init_library` function.

The call and the callback are asynchronous to prevent the call from blocking the calling thread.

## Implement the callback

Implement the `initialization_CB` and pass this as a parameter of the `init_library` call. For more information on how to do this, see [Implement callbacks](/point-of-sale/classic-library-deprecation/classic-library-integrations/c-library-integration/calls-and-callbacks-c-library/implement-callbacks).

### Parameters

| Name          | Description                                                                                                                                                                    |
| ------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| `result`      | Returns the result of initializing the library. The result of initialization is always zero.                                                                                   |
| `echo_struct` | A pointer to a user-defined struct that is echoed back in the callback. Use this to share a POS data struct between the call to the library and the callback from the library. |

### Code example

```cpp
void initialization_CB(void *result, void *echo_struct){app_context_t * POS = (app_context_t *)echo_struct;
printf("library is initialized");
}
```

## Allocate request structure

Use `init_library_allocate` to allocate memory for an `init_library_request` structure. Populate the `init_library_request` by performing string duplication to fill heap-allocated strings.  The library automatically frees this memory.

## Call the init\_library function

Call the `init_library` function with the provided parameters to initialize the library.

### Parameters

| Name                | Type                                                                                                                                                         | Required                                                                                    | Description                                                                                                                                                                   |
| ------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------ | ------------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `initReq`           | Struct: [init\_library\_request](/point-of-sale/classic-library-deprecation/classic-library-integrations/c-library-integration/structs/init_library_request) | ![-white\_check\_mark-](/user/data/smileys/emoji/white_check_mark.png "-white_check_mark-") | A pointer to the `init_library_request` struct, this struct contains all the input parameters for this call. Allocate this request with init\_library\_allocate.              |
| `initialization_CB` | Function                                                                                                                                                     | ![-white\_check\_mark-](/user/data/smileys/emoji/white_check_mark.png "-white_check_mark-") | A pointer to the callback function in the POS that the system returns with the results of the initialization call.                                                            |
| `echo_struct`       | Struct: [echo\_struct](/point-of-sale/classic-library-deprecation/classic-library-integrations/c-library-integration/structs/echo_struct)                    | ![-white\_check\_mark-](/user/data/smileys/emoji/white_check_mark.png "-white_check_mark-") | A pointer to a POS-defined struct that is echoed back in the callback. Use this to share a POS data struct between the call to the library and the callback from the library. |

## Get the function call result

`ADYLibraryResult` is used to store the result of the function call, the immediate response to the call. This is an enum that indicates if the system received the request. Should be `ADYEN_OK`, if this is not the case, something has gone wrong. In this case, check the input to the call and if it cannot be resolved, log the result and contact [Support Team](https://ca-test.adyen.com/ca/ca/contactUs/support.shtml?form=other)

This is not the final result of the call. The library returns the final result in response to the library initialization call.

## Handle the callback

The POS needs to wait for the initialization callback before continuing with other functions, like boarding the POS systems and PED devices, and performing transactions.

### Parameters

| Name          | Description                                                                                                                                                                    |
| ------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| `result`      | Returns the result of initializing the library. The result of initialization is always zero.                                                                                   |
| `echo_struct` | A pointer to a user-defined struct that is echoed back in the callback. Use this to share a POS data struct between the call to the library and the callback from the library. |

## Code example

```cpp
typedef struct {
  char *user_data;
} app_context_t;

// result is always null for initialization callback
void initialization_CB(void *result, void *echo_struct) {
app_context_t * POS = (app_context_t *)echo_struct;
printf("library is initialized");
}

main()
{
  app_context_t POS;
    init_library_request *initReq = init_library_allocate();
    initReq->pos_name = strdup("Adyen");
    initReq->app_name = strdup("Adyen");
    .
    .
    .
    ADYLibraryResult result = init_library(initReq, initialization_CB, &POS);
}
```