What type of declaration is "static const struct bt_data ad[] = {X,Y,..}"?

Question

I am.a beginner in BLE embedded development, and I have a question regarding the following declaration that is going to be "the advertisement data" In specific,

static const struct bt_data ad [] = { 
 BT_DATA_BYTES ( BT_DATA_FLAGS , ( BT_LE_AD_GENERAL | BT_LE_AD_NO_BREDR )), 
 BT_DATA ( BT_DATA_NAME_COMPLETE , DEVICE_NAME , DEVICE_NAME_LEN ), 
 }; 
 I know that ad[] is an array, but I am confused regarding what is before that. Typically, I expect from the C language syntax that a data type should be placed prior to the name, but here there is something between " struct " and " ad ". Any help or idea is much appreciated. Thanks.

Naeem Maroof · Accepted Answer

Hello, 
 Thank you for contacting DevZone at NordicSemi. 
 The line of code that you have mentioned: 
 static const struct bt_data ad[] = {}
 
 is declaration of an array. 
 The name of array is ad 
 The type of array (or the type of data it can store) is bt_data 
 where bt_data is a struct that has been defined in header files. 
 
 In the sample code (e.g peripheral_uart) opened in the VS-Code, if you hover over the bt_data , it will show you its description 
 
 Moreover, you can right click on bt_data and goto the definition of where the struct is defined in the header file. 
 
 So here you see that the bt_data is struct defined in bluetooth.h and its subfields are as shown below:

Hope it answers your query. 
 
 BR, 
 Naeem

Naeem Maroof · Answer

Hello, 
 Right. The question is related to the C language itself rather than NCS or Nordic solutions. 
 This could be the limitation posed by the language. Please have a look at this discussion , and following pages which talk about the same. 
 Struct in C vs C++ 
 Different struct variable declarations 
 
 BR, Naeem

What type of declaration is "static const struct bt_data ad[] = {X,Y,..}"?

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